330 Reports and Proceedings — Geological Society of London. 

 S-IBI^OS-TS J^Z>T3D I=I^OG:H]:E3IDII^^C3-S. 



Geological Society of London. 



I._May 18, 1898. — W. Whitaker, B.A., F.R.S., President, ia 

 the Chair. The following communications were read : — 



1. " The Garnet-actinolite Schists on the Southern Side of the 

 St. Gothard Pass." By Professor T. G. Bonney, D.Sc, LL.D., 

 F.R.S., V.P.G.S. 



The author describes the field relations and the microscopic 

 structures of a group of schists or gneisses characterized by the 

 frequent presence of conspicuous garnets and actinolites, which are 

 exposed on the southern slopes of the St. Gothard Pass and for some 

 distance west and east, on the northern side of the Val Bedretto. 

 These, called for purposes of reference the Tremola Schists, he has 

 examined from time to time since 1878, the last occasion being 

 the summer of 1897, when he was accompanied and aided by 

 Mr. J. Parkinson, F.G.S. These rocks in the field might be 

 regarded as highly altered sedimentary strata (as the author once 

 thought) or as a group of igneous rocks (originating possibly in 

 magmatic differentiation) affected by fluxion-movements anterior to 

 consolidation. To the latter view he now inclines, but considers 

 the schistosity and the peculiar minor structures to be the results 

 of crushing (generally without marked shearing) followed by very 

 considerable mineral reconstruction. The garnets he holds to be 

 anterior to this crushing, but the larger biotites and the conspicuous 

 actinolites to be posterior to it. These minerals, in his opinion, 

 throw some light on processes of crystallization in rocks more or less 

 pulverized, or, in other words, in the presence of various impedi- 

 ments. He thinks it probable that the Tremola Schists assumed 

 their present form prior to the great Tertiary earth-movements 

 which gave rise to the existing Alpine chain. 



2. " On the Metamorphism of a Series of Grits and Shales in 

 Northern Anglesey." By Charles Callaway, M.A., D.Sc, F.G.S. 



These rocks occur in a patch about three miles square, situated 

 south-west of Amlwch, and extending from Llanfechell and Ehos- 

 beirio to the boundary fault near Melin Pant-y-gwydd, and from 

 Mynydd Mechell to Bodewryd. They dip to the north, and ap- 

 parently form a series in the following ascending order : — (1) Highly 

 quartzose and gritty rocks. (2) A considerable admixture of softer 

 beds (hypometamorphic shales). (3) Predominating shaly strata 

 with gritty seams in subordinate proportion. The lower beds 

 contain intercalated seams of well-foliated micaceous or chloritio 

 schist, and in these lower beds the signs of compression and con- 

 tortion are most marked. 



A series of microscopic slides from Ehosbeirio, Llanfechell, 

 Pant-y-glo, and intermediate localities links together the fragmental 

 rocks with the true schists. Grains of clastic quartz are replaced by 

 " granular particles fitting into each other with foliate interlocking 



