the miocene trees of the rocky mountains

The Miocene Trees of the Rocky MountainsAuthor(s): T. D. A. CockerellSource: The American Naturalist, Vol. 44, No. 517 (Jan., 1910), pp. 31-47Published by: The University of Chicago Press for The American Society of NaturalistsStable URL: http://www.jstor.org/stable/2455701 .

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THE iMIOCENE TREES OF THE ROCKY MIOUNTAINS

PROFESSOR T. D. A. COCKERELL

UNIVERSITY OF COLORADO.

THE living arborescent flora, of the Rocky -Mountain region is at the present time occupying the attention of a number of able workers, including Nelson in Wyoming, Rydberg of the New York Botanical Garrden, Sudworth of the Forest Service, Ranialey, Bethel and Scineicler in Colorado, Wooton in New Mexico, and others. As a ie- sult of all this activityN, we are promised two manuals of Rocky Mountain botany, and a third of trees alone, so we slhaill have three separate and independent treatineilts of our woody flora to comnpare and choose fromt.

Unfortunately, those who have been so active and ex- haustive in their investigations of the living flora have not ca-red, as a. rule, to consider time historical or paleo- botanical side of the subject. Alany,- "recent" botanists seem to have a positive dislike for fossil plants, and few ml-anifest any great eagerness to receive information about the .ancestors or predecessors of time species which occupy their attention. Like all enthusiasts, the writer is filled with the idea that. the matter has only to be ade- quately presented to connuancd universal attention; and hence offers this discussion, not, so nmuch for the paleobotanists as for those students of living plants whose active interest. may be aroused in the problems involved.

Goimlg back fromt the present tinle, we are practically without information concerlinlg the plants of our region until we come to the Florissamlt beds, assigned to the Miocene. These beds, however, contain a.n abundant series of remains, mnlany of the plants beautifully preserved, as the accompanying illustrations show. They testify to a clililate both warlmler amnd damper thaan that of the present day, time arboreseent genera illcluding Sapindus, Ficus,' Diospyros, Persea, Leucmna, Amlona,

1 The determination of Ficvas is based on the leaves. In confirmation of I) 1 0>



32 THE AMERICAN NATURALIST LVOL. XLIV

etc., but so far as known no palms. Some, as Alilanthus a6m6.e ricatniat, pertain to generaI now restricted to Asia.

The determination of the age of the Florissant beds hias been a matter of some difficulty, notwithstanding the large nmumtiber of organisms preserved. Comparing the flora with that of the European Tertiary, I have felt satisfied that it should be referred to the Miocene, and probably to the Upper Miocene. The resemiblance to the flora of CEningoen in Baden, known to be upper -Miocene, is most striking. Thus we have the following parallel or representative species:

Florissant. (ningen.

Liq aidame ibar convexainm Ckll. Liejaidambar eCur1o0)) -cu A. Br. UlMus brantnii Heer, Lx. Ulinus birnjii Heer. Cnvpto,)tia insignis (Lx.) Ckll. Comptovlia mninycnsis A. Br. Poriana spiruii Lx. Po arna muninycns is A. Br. Poratna, teonis Lx. Porana mnacrantlta Heer. Acecr florissanti Kirch. Acer tricuspidatuern A. Br.2

Many others could be cited. On the other land, the Florissant incense cedar, Ucyderia or Libocedrtts colo- rademisis Ckll., is to be compared with H. salicoritioides., of the Lower Miocene of Radoboj in Croatia. The Florissant redwood, Sequoia hltadewmi (Lx.), is iiot, related to S. st~erab~e'yi Heer from- & ingen, but to S. langsdorfi (Brg-t.) Heer of the Swiss Lower Nliocene; this species, however, survived into the Upper -Miocene in Italy and Gal icia. This S. leanysdo/fit has been recognized in America also from the Upper Cretaceous to the Miocene, and some, of the Florissant specimens have been referred to it; but the identity of the plants from so many diverse localities aiid horizons is qtuestionable, and from Floris- sant I think we have only one species, S. haydeni.

The Sequoia and Libocedrus of Florissant are both verv closely, related to their living Californian allies; so it cones a discovery by Mlr. Bres, wvho in working over the parasitic Hynien- optera from Florissant has conie Upon what appears to be a genuine fig- insect,. apparently of the South American genus Tetrapus Alayr.

Acer trilobhotum (Sternh., 1825) A. Br., 1845; not A. trilobatum Lam., t1 Se.



No. .,17] ,JJJOCENLI riu xREES 33

much. so that one is in some difficulty to point out any tangible diffterences. This is equally tiue of a number of other cases, of which the following are illustrative:

Florissant. Living. Pivus wheeeleri CHiii. PiPh s flexilis James. Pinus- stargisi Ckl1. 1Pinus tccda L. ,1 ;1((fltlus (lanVtericauI C(kil. A1ilanth us glandutlosa 1L.

(Savwb uCScus wtoni CHll. 8am b ucuts arboresens Nutt. ,.4nonac spo)liaca CUll. 111ona glabra L. J,'obin ia brittoni CHll. JRobiiia psesudacacia L. PopClts lesqJerevxi Cx (l. IO])Ullus c(ngytifobia James.

Q uervCU c /i)atif( rn is (Ckil. Qu(2 UrC us i ivCl a a WXalt. -S'lvJus coloi1lradensis C1k11. SalividUes drumm)nondi H1. & A.

So numerous are the reseinb}8nces to the living flora that one igllht well feel persuaded to refer the beds to the Pliocene-certnaily better there than to the Oligocene or Eioeenee! However, the Flol.s.sant fishes, with the exception of Amia, nre of extinct genera, and no less than 17S geniera of insects are su]pposed to be extinet. For a variety of reasons, based chiefly upon a study of the insects, I believe timt the F]oiissant pel iod corre- spouids with )Ol)1ori 's "Fifth Fmmalm Phnase' (Bull. 361, IT. S. Geol. Survey), ill which a. ine fauna was in-vadiing the coumtrv flion Elmiasin, wvlile conlnlectioll wi ti Soutfi

America, had ii-ot, vet been established. Some of the Ftlori2s aint groups of illsects, slite as the ApdiClidaf and B-oilbyOliidL, seeni to represent tbe original A imeican famuna uncontaminated; awhile others Sbow old world ty)es, the miost significaiit land interesting of whidel is the tsetse fl-v (Glosssh) . b Oshoinu's "Fifth Plitmse" in- cludes the MAiddle amd Upper MAioceene, aiid so far as meay be judged, IFlorisstmt should belong near the iiidcldle of it.

The attempt to correlate the Florissanit beds with other American flortas ascribed to the Mtiocene brought. out a number of difficulties. With the exception of tHe little-

A second species of tsetse fly, Glossiva osborn i (Rli., lois leeii recently discovered. It is onily 10, -mm. long, the wving', 7 mmn.; the voention is normal

for the genns, hnt the first hasal cell bulges less snhapically than in Scud-

der 's species.



34 THE AMERICAN NATURALIST [VOL. XLIV

V~~~~~~

FIG. 2. Weinmnannia lesquereuxi Ckll. FI(. 1. WVehinmannia phenacophylla Ckll.

known formation at Elko Station, Nevada, I do not find anything which really seems to correspond with Floris- sant. According to the theory outlined above the Mascall beds of Oregon, which possess -a varied flora, should be either contemporaneous or (more probably) somewhat earlier. Fortunately, fourteen species of mammals have been obtained from the Mascall, and these place it rather definitely in the Middle Miocene. Considering, therefore, a probable moderate difference in time, combined with noteworthy geographical and altitudinal differences, we ought to find the Mascall flora similar to, but by no means identical with, that of Florissant; and this is exactly what comparisons show.

Thus of the 77 Ma-scall plants (nearly all trees) referred to definite genera, no less than 56 are congeneric with those of Florissant. Of those not congeneric, five are so dubious that they have not been specifically determined. The Mascall genera not yet found at Florissant are the following:

1. Equisetum.-This has no significance, as it abounds in Colorado to-day, and must have been present during the Florissant period.



No. 517] 1110 CE.AITE TREEAS 35

2. Ginkgo.-iRepresented in the Mascall by a fragmlIent not specifically determined. This genus is not knowii in the Rocky Mountains later thatn the Laramiiie and Liv- ingston, on the border line between the Cretaceous and Tertiary. As is well known, there is a. single living (Asiatic) species.

3. T'huites.-A fragment not specificatlly determined. It is practically identical with T. eh..reusiuardi. Heer (Miiocene of Sachalin aind Spitzbergen), but that plant appears to be referable to the mtiodern genus Chl iamTlecy- paris.

4. Glyptoshtobuts.-A genus still livingl iii China. It was supposed to occur at Florissant, but I believe the material so referred all belongs to Sequoia. The AMascall material is not above suspicion of also being Sequoia; indeed Lesquereux so referred one of the specimens.

5. iaxodihutrn..-The Mascall specimens are referred by Knowlton to the widely distributed T. distichwinio- cenum Heer, which should be called Ta.Xo ditm distichum dtt biumi Taxod'itnz, urnduWiu (Sternb.) IlHeer, originally described from Bilin. This differs from Sequoia by th!e deciduous leaves, which are not decurrent at the base as in Glyptostrobus. The genus still lives in our southern states.

6. Artocarap's. -Represented by very fragmentary material, doubtfully referred to A. califor'nica Ku.

7. Malgiol-ia.-Major Bendire collected a plant which Knowlton says "''ay well be" Mll. hi glefieldi lHeer. It has not been obtained by recent collectors. JMagnxl)oliaM; daya-na Ckll. ned. (31. l6{anceolata Lx. 1878, niot Link. 1831) is listed by Knowlton as from the ascall], but in his detailed account lie says it. is from Cherry Creek, which should be Lower Eocene.

8. Lauctirns.-Florissant has a species of Persea; Laurus and Persea are allied, and not distinctly separated by paleobotanists.

9. Platanuts.- The MAaseall ,specimens appear to belong




j.

F'IG. 3. Scqudic hi(ydeni (Lesquereux). Redwood.

to three species, but none are sufficiently well preserved for positive specific identification.

10. Prtinus.-The two Mascall species described by Knowlton are only doubtfully referred to this genus, which is of course abundant in the modern flora.

11. Rulac.-Generic reference rather uncertain; the genus is scarcely separable from Acer, which occurs at Florissant.

12. lsculus.-This well-known living genus is repre-



No. 517] 31I0(!ENTE 1i1RLEKljS 37

sented in the Mascall by leaflets which closely reselnl)le a.n un1cdescribDed Florissant species which may be a Ber- beris, u)llt is certainly not an 3]scnulns.

12.') . Grceiu.--The lilascal] pla-tnt irS reerred yl ) owl - ton to Cf. (l'Jenll-(t( (1l)nger) Hleer, Avlieh occurs in Emurope at ( Eningen.4

Tri'tee other geniera, Plui1anguites., (_'yvper'a(ctites anid

Sn ila, care nion- arbor-escent, and ltlhi-aTe no partienlar sigu-

niificance. Thns it would appear that in the MALiddle AMiocellne

period Ginikgo and (Hyptostrobns if we may accept the determinations hadc not vet retreAted fvoni the Amer- icanl continent, hut snrvived at least in the northwest. For the rest, the Alascall flora is no doubt a lowlanld onie as conln)ared with that, of Florissanit, and thlis aloe would explain mianly of the difterences; thus, nO onle wonld expect to find Taxodlinll growing around a. mounontain ]<lae.

Dr. Knowlton has described (MAlonog. IT. S. Geol. Sur- v\ey\, Vol. 32,-part 2) an extensiv-e flora ftoun the Yellow- stonie, which hle regards as Miocene. Tlhe fossil phInuts of the Yellowstone National Park are divided blNT him inlto three series: (I) Fort IUnion, which is Basal Eocenie, (2) Intermiediate, said to be AMiocenie, an1d (3) LauniaICr Flora, also MNiocenie. With the first we atre not now coin- cerned, 'but the others iniust be compared with the flora of FlSlorissanlt. Considering the relative proximi-ity of the Yellowstonie beds to those of Colorado, onie would expect to find much similarity -aned even idenititv\ ini the ptlcalnts; but this is nlot the case. The difterence of locality, with l lnolderate difference in tiue, might perhapscl acc('ounlt for the diversity. of species; bnt the YAellowstone flora as a whole does not impress one as bAeing1, so Modern as that of the ]\[ascall beds or Florissanit, while there is a sig(V- nificant ideotnit of species with those of time Eocene.

I have extracted fromi Kuiowlton's tables a list of all the Yellowstone ''Xliocene" ne lanits said to occur else- where or inl the Focenie, with the following result:

The African G evia crenala Hlochlst., 18S8 (ilot Uinger, 1S50) i tahes tHi Ganie G. pop ulifoTia Valil, 1,790.




FIG. 4. Rhu8 corarioiudes Lesquereux. Sumach.

1. Common to Fort Union (Eocene), Intermediate and Lamar.

Sequtoia langsdorfii (Brgt.). Said to go down to the Laramie (Cretaceous).

Juglans rugosa Lx. Goes down to the Laramie. Castanea pulchella Kin. Ficits densifolia Kn. Laurus californica Lx. Also auriferous gravels

of California. Laurus grandis Lx. (not Wallich). Also aurif-

erous gravels of California. Platanius guillelenc Gopp. Perhaps also Laramie. Aralia notata Lx. Also Denver beds. * Eleodenidron polymo rphum Ward.

2. Cominon to Fort Union and Intermediate. Equtisetumin canaliculaturn Kin. Perhaps also in the

Lamar.



No. T]2 30MIOCEATE TREES 39

Magnolia (?) pollacrdi Ku. ' Ulntas minimal WTard ? Sapindus affinis Newby.

3. Comnimon to Fort IUnion and Lam-nar. A spienzi 'tam iddiuzgsi Kn. L,_jodium kcnqdl/ssi Heer. Eqaisetmin dec~iiwam IEn. Jagla-,ns crescentiaw Kun. Ficvs asimitimefolia, Lx. Also auriferous gravels

of California. Laerals primhigeuia linger'?9- illU,]nftl.flct lama.irenwsis Ku. Sapind)'(lvs gr andifoliolas Ward. Sap]inl(Us ward-li Kin. I licon, a entiqva, (Newb.).

'Ulhnus pseCd?-otdfeva Lx. ? Those marked with an asterisk occur in the Fort Union

only outside of the Yellowstone. 4. Common to the Intermedate and the Denver beds

(Basal Eocene). Osmantotda, af/inis Lx.

5. Common to the Lamar, Basal Eocene and Laramie. RBhalmav s rectinervis Heer, Lx. Heer describes

this from M\ Ionod, in the Lower MAliocene; we may venture to doubt the identity of the American plant.

Thus we have twenty-six plants specifically identical with those of the Basal Eocene.5

G. Common to Lamar and " Green River " of Knowlton. (See also under 7.)

Salix eloneetat 0. Web). Said to occur at Elko Station, Nevada, but represented only by un- characteristic fragments. The determination of

5 The laseall is supposed to have five species cOlliflOll to the Port Union; but of these two are doubtful, two others are the conifers Sequoia longs- dorfibi alldl Toxoclineo, while the fifth is Sopidicls obtesifolies, to Awlhicelh a sl0gle specimen from the MAasenall seemss to belong.'' S. obthsifoliios was originally described from beds supposed to belong to the WashalIde (Later PEocenie).




T~~~~~~~~~~~~T

1~~~~~~~~~~~~~~~~~~~~~~~~~~~1

FIG. 5. Ulmius hillit Lesquereux. Elm.

the Lamar plant is considered doubtful by Knowlton.

Fagus (Fagopsis) lon gifolia (Lx.). Elko Station, Nevada; Florissant (very abundant) and Eocene (?) of British Columbia. The British Columbia locality is on the Similkameen River, whence come various fossil insects. Dr. Daw- son (quoted by Scudder) considered these de- posits Miocene. The Yellowstone collection in- cludes about forty specimens which Knowlton



No. 517] 110 CENJE TREE'%S 41

refers here, all from Fossil Forest Ridge. This is, undoubted\] 7, a distinctively MAI i oce plaiit, aiicl must be accepted as pertinent, evidencee. The determination must be presumed t(-) be Correct though it nay) be poiitecl out that vTariolus other leav\.es have almost exactly-- the same veiiatioii and appearance. rphis is especially true of the species of Zelkoval to Which geiiiis Engler (I894) actually referred F. longlifoolia, though the discovery of the fruit has siiice shown that it is iiot related th ereto. Ulmnits piwriue' u ia, as figured by Ileer from Alaska, is also almost exactly like F. lo n gifola;

it is conisiderecl cloubtfull] Eoceiie, but Kn-iowl- ton has recognlized it in thee MAascall (AMtioceiie). From the shape of the base, aiich other features, it seems to nie certain that the Alaskaii plhait is ilot the original U). p ierinri'," of which linger

gives four figures iii the (liloris Protogma. The latter is decidedly more elm-like inl a-ppearance.

Cory1its mctcqctjarr'ii (Forbes) Heer. This plant, ,as recogiiized in Am<erica, is a Fort Iliiioil and possibly Laramie species; recorded also from the Eocene ( ?) of Alaska.

Diospyros brachtysepa-la A. Br. As recognized in this country, this is a Laramiie and Fort Unioii species; the record fron-m Florissant I believe to 1e erroiieo us.

None of the aabove belong, to the geiiuiiie Greeii R;iver series; three are quite without signi-ficanice as inidicatiig AMioceiie affiiiities, but the Fagls stiids out as a solitary AMiocene representative.

7. Commonii to the Lamair aund the Auriferous gravels of Califormia. (See also under 1 aincd 3.)

Jglltla,,n;s leoanis Ckll. Two specimens iii the Lamlar. Popluths balsamowoides G6pp. Also 'Miocene ( h) of

Alaska. Known in the Yellowstone only from ai fragment, which certainly ca!n not be positive] \v determined as l)alsa)w mides: in fact, it shows




FIG. 6. Myrica drynteja (Lesquereux).

some differences, at least as compared with the original European balsamoides, which ought to be specific.

Sa~lix varrians G6pp. Eocene (i?) of Alaska. The Lamar plant is a fragment, and according to the figure, the margin is quite unlike that of the European variants.

Salix angusta A. B. Said to occur also in the Basal Eocene and true Green River. The Lamar material consists of doubtful fragments.

Quercus furcinervis americana Kn. Ficus shastensis Lx.? Ficus sordid. Lx. AH mere fragment from the

Lamar. Ficus asiminafolia Lx. Very indifferent material

from the Lamar. Also Fort Union. Magnolia californica Lx. ? The Lamar plant is

represented by a single specimen, "so much



No. 517] MIOCENTE TREE S 43

broken that its positive identification is not pos- sible ' (Knowlton).

Persea pse udocarolilneusis Lx. The Lamar speci- nmen figured, "'the best one founncl," consists of the upper half of a leaf; what there is of it appears to agree with the C aliforniian species, although it has more lateral viens.

Rhus nixta Lx.? Aralia whithieji Lx. Also in the Intermediate.

None of the Yellowstone specimens are perfect, bnt they appear to belong to this hanldsolmie species.

Tlus the species common to the Lainar and Anruriferous glravels, butt !tot known;i fromi Basal Eoce~ne, are few, and in several cases of doubtful identity. ALts the reference of the Lamar to the _Miocenie rests wholly on the resemn- blanice of the flora to that of the Auriferous gravels, with the exception of the indication afforded by Fqg us lonyq- folia, it must be considered at least somewhat dubious. It is also to be remlalrked that eleveni species of plaints are supposed to be common to the Yellowstone Fort Union and the Auriferous grav\els, although two of these, at least, are doubtfully from the gravels, while in four or five cases the Yellowstone material is fragmentary or doubtful.

It is omme thing, however, to recognize distinct elements 1in cominon between the Auriferous gravel>s amid the Lamar, and another to prove e the latter AMiocene thereby. The former may be conceded, the latter I think Inot.

Lesquereux enunmerates thirteen species from the Au- riferons gravels which are almost identical with living species; he also cites seventeen which are evidently, but not vTery closelT, related to living ones. Of the thirteen, four are enumerated from the. Lamar; of the seTellteen, not one. Of the fonr comnnon to the Lamar, three are cdnbions, and only Juglans leomis (a species represented to-dayv by the Asiatic J. regia) appears to be of satis- factory standing.



44 THE AMERICAN NATURA-ILIST [VOL. XLIV

FIG;. 7. Popululs crassa ( Lesquereux ). Cottonwood; probably fruit of P. 1MIcllcmixlzwi.

FIG,. 8. Populus lesquei^ciixi Ckll. Cottonwood.

Four species of the Auriferous gravels a-re said by Lesquereux to be identical with Miocene plants, but are all unsatisfactory, as follows: (1) F+agus an-tipofii per- -haps goes to the Laramie, and the Californian specimen was only half a leaf. (2) Populous zaddachi; supposed to go down to the Basal Eocene. (3) Fic-us tilicefolia;';

.4~q

FiGl. '.1. Sal-s }m aelcy Ck1. Willow.

a Ficus tilicfolia (A. Br.) Heer, 1856, has priority over F. tiliafolia Baker, Jn. Linn. Soc. 21: 443 (1885), from Madagascar. The latter may become Ficus bakeriana n. n.



No. 317] iI IOCI ONE TRELES 45

said to go down to tbe Laramie. (4) Azbrlic-a zddaclui; of uncertaini determinatioll, olle of the specimens was Pla.tanCuts dCssecta. None of these is found in the Lamar, but F'.. (tnt'jtpo/tu is in the Yellowstonie Fort Union.

Eight other species from. the Auriferous gravels are stated to be allied to MAioceNIe species, five of these being, also related to living plants. OIne of the five, Juglam"s or(cyoXniana.O, has since, proved to be from the Mlascall, and not to occur in the Auriferous gravels. The other three are as follows:

iC.1.l So S1ida Lx. Allied to, or perhaps identical Witll lin.,J -t,1(e1i -, of G-CTeelland.lO 1tfln with, F. gf iwnandilca fGenad A f rag-

inent. referred to tbis has been found in the Lamar. mIC118 MleSla Il. I0. (F. )UP3o/)lqf lie. Tax., IStS, niot

Salzui., Mart. FP. Braz. 4: 93). Allied to T'. p}ianicos t[l bu.t this is a species of the BaIsal FMocene and tLaaui~ie. re(icz 'l tcweji lix., said to be allied to ani Evcans- tonl Species, wb liich- womil dbe Eocene.

It is thus apparvenIt that the Auriferous gravels flora has nio decisive MALiocenle affinities, but is composed of two sets of plants, one related to I vinig forms, the other to those of the Ejocene. It is huown to be a mixed lot, anlld whben I recently suggested to :Dr. J. (C. -Merrian, of the University of Californlia that it mighlt perhaps be partly Pliocene and partly Eocene, lie replied that this might indeed be the case.

It. is further to be remarked that K-nowlton formerly].\ ],egardedl the MAc2ascall flora Las hav.-Ting affinity with that of the Auriferous gravels; but lie subsequently discovered that certain of the species lie had nmost relied on were really confined to the AlMascall, and did not occur in the gravels at all. "''llis correlation therefore fails, " lie states, and the absence of relationship. stands as an argu- ment. against the MNliocenie age of the gravels.

Tlhe conclusion seems to be legitimate that the Yellow- stone -Intermediate and Lamar florm a~re UJpper Eocene, or at least older than -Miocene. Were they really Mio-




FIG. 10. Ptelea modcsta (Lesquereux). FIG. 11. Melia expulsa Ckll.

cene, with so much resemblance to even the Basal Eocene, the Florissant flora, to get as far on the other side as its lack of affinity would suggest, would have to be projected somewhere into the future! If this opinion is in any degree correct, Florissant remains as the only Rocky Mountain locality for Miocene plants, so far as known.

The accompanying figures, all taken from specimens obtained at Florissant by the University of Colorado ex- peditions, will give a good idea of the material from that locality. Nowhere else in America are Tertiary plants so well preserved. As compared with the Eocene flora, and especially the Basal Eocene, the Florissant trees are more diverse in type, with usually smaller leaves, which are often compound. Excessively moist conditions are not indicated, though there was evidently much more moisture than at the present day. Some of the plants are even somewhat xerophytic, indicating that the higher slopes may have been relatively dry. Osborn remarks on the evidence of increasing summer droughts



No. 517] M1IIOCENE TREES 47

in the AMiddle AMiocene. So far as the mammals are con- cerneci, this is chiefly indicated by the plains f auna. Ow- ing to the generally higher temperature, the air was probably mnoister than at present, but the moisture may have carried farther, to be precipitated oii the mountains. Thus the conditions oii the plains and towards the sea may1 lhave resembled those of Soutliern and Lower Ctali- fornia to-day, with a comparatively damp atmosphere but little or no preciptation during a considerable part of the year. The desert fauna and flora of the southwest is a highly specialized one, which has certainly not. comie into existence since the Miocene, at least. as regards its fundamental types; so it becomes necessary to postulate a desert region during Miocene times, and no doubt mnuch earlier. Whether we shall ever know mnuch about the Tertiary deserts from fossil remains is perhaps question- able, through we certainly, have evidence of a semi-desert fauna, as is illustrated by the large tortoises of the -Upper Miocene. The Florissant beds afford us a wonderful insight into the mountain life of the AMfiocene, and must have a continually increasing significance in relation to the evolution of the fauna and flora, of this continent. Lost unfortunately, they have as yet yielded no recogniz- able mammnalian remains, but I am convinced that these will eventually be found. Tlme beds are far from being exhausted, and comparatively little digging lmaIs been domie at. the place where fragmemmts of a mammmmal were obtained-a locality which I shall be glad to describe in detail to any omie wvlo cares to go and try his luck. In the meanwhile, large collections both of plants and of insects, already obtained, remain to be investigated amid re- ported upon, but for various reasons the work proceeds slowly.



the miocene trees of the rocky mountains

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