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VISIT TO MISS M. S. JOHNSTON'S GEOLOGICALCOLLECTION.

Saturday, 10th February, 1940.

Report by ARTHUR L. LEACH, F.G.S.

VERY nearly on the 25th anniversary of a former visit (6thMarch, 1915) to Miss Johnston's collection, then at

Hazelwood, Wimbledon Hill, members of the Associationassembled at No. I Cumberland Road, Kew, to examine hergreatly enlarged collection, now enriched by thousands ofspecimens gathered in the intervening years in many parts ofthe world. Mr. R. E. Crossland and one other member of theparty recalled that they had been present on the occasion of theformer visit, one also made under the shadow of war.

Miss Johnston has most admirably used her many oppor­tunities for foreign travel. Wherever she has gone she hasassiduously collected rocks, minerals, fossils and, whenever shehas been among peoples who retained their native handicrafts,she has obtained specimens of articles made for domestic useand personal adornment-articles that are slowly but surelybeing superseded by the spread of machine-made mass-produc­tion products. Her collections have not been stored up inuseless privacy, but have always been made accessible to personalfriends and to groups of people who showed any interest ingeology, archceology or ethnology.

On this occasion Miss Johnston had set out a very largenumber of specimens chosen to illustrate the following aspectsof geology:-

A. Choice specimens of minerals, e.g., felspar, tourmaline, asbestos,fluorite, malachite and selenite.

B. Ferruginous, siliceous and calcareous concretionary structures.e.g., cone-in-cone, septarian iron-nodules, "poached egg"concretions of Oligocene chert, from the Theban Mountains,dendrites, stalactities and stalagmites, pseudo-organic forms fromthe Magnesian Limestone of Fulwell Hill.

C. Illustrations of alterations produced in rocks by beach-action,sands and pebbles: wind and sand-blast in the Egyptian Desert,e.g., facetted pebbles, "dreikanter" (three-edged) and "wind­kanter " (wind-edged) : chert nodules split and faked by tempera­ture changes; striated stones from glacial drifts; rocks slicken­sided, crushed and crumpled by crustal movements.

D. A large series of photographs (mostly enlargements from MissJohnston's own negatives) of scenes in the Colorado Canon, theBad Lands of Arizona, the Rocky Mountains in Canada, Spainand Majorca, the French and Swiss Alps, the Canary Islands, theTheban Mountains and Egyptian Desert, the Great Karroo and theVictoria Falls of the R. Zambesi.

VISIT TO 1\1ISS 1\1. S. JOHNSTON'S COLLECTION 20g

E. The most numerous specimens were chosen to exemplify the forms,conditions, weathering and decomposition products of hydratedsilica in such minerals as flint, chert, agate and chalcedony.Flints collected from the North Downs and other Chalk areasdisplayed (I) the development of patination by chemical andphysical changes, from white spots to a kind of basket-work inter­lacing of white streaks and finally a complete bleaching of thesurface. (2) the superficial staining of the patinated (and there­fore porous) surface by iron-bearing solutions to various tints ofyellow, red, brown. (3) the superficial staining of the surface bycontact with red soils, metallic iron in ploughshares, etc. (4) thepenetration of chemical changes into the interior of the flints andthe subsequent formation of ochreous bands by ferruginous infil­trations. (5) the further extension of chemical changes by thesolution of silica until the whole of the flint pebble is affected as atKnockmill, on the North Downs above Otford, where the Black­heath Beds yield pebbles ranging from normal black through greyto pure white lumps, finally breaking down into white grittymasses of siliceous powder. (6) Alterations produced in nodulesof Oligocene chert by rapid temperature changes in the Egyptiandesert region where pebbles and concretions are split longitu­dinally into thin wedge-shaped slices sometimes barely one-eighthof an inch thick at the butt-end. Such fractured nodules may befound embedded in the desert sand and, by carefully collecting theslices, they may be recombined to restore the original form of thepebble or concretion. Side-by-side with these sliced chert noduleswere some pebbles of Chalk split longitudinally by recent frost­action and collected near Ipswich. (7) A large series of flintpebbles and nodules with curiously pitted surfaces. Such pittedflints may show only one hollow, bowl-shaped and about as largeas a farthing or a halfpenny in diameter. But often the surfaceshows numerous pits sometimes so close together that their marginsintersect and a curious cellular structure is produced not unlikevery coarse honeycomb. Such pitted flints occur most notablyalong the North Downs and a few other places such as KingsleyVale near Chichester. The pitting has probably been caused byfrost action, but not in recent times.

After the party had suitably expressed the pleasure theyhad derived from Miss Johnston's kindness in displaying so manyof her remarkable specimens they were entertained to tea anda very pleasant afternoon came to an end.