JReporf.-i and Proceedings — Geolcxjieal Soeief// of London. 235 



Lake Baikal appears to be of recent origin; it is 4,500 feet deep, 

 and has not been filled by the great quantities of sediment brought 

 down by the Selenga and other rivers. Although glaciers could 

 frequently be seen on the mountains which border the Central 

 Asiatic Plateau to the north-west, there was no evidence that the 

 glaciers had ever deployed on the plain. The loess-region of 

 Turkestan, and indeed the whole area from the Sea of Aral to the 

 Black Sea, appears to have been recently elevated, in some places as 

 much as 3,000 feet. Desiccation took place at the same time, so that 

 the larger lakes are only brackish or still fresh. Direct evidence of 

 this in the form of deposits is given. The author thinks it likely 

 that the absence of glaciation in Northern Asia may have been due 

 to the rainlessuess of the region, and that while America was 

 elevated, Asia was depressed during the Glacial Epoch. 



2. "The Hollow Spherulites of the Yellowstone and Great 

 Britain." By John Parkinson, Esq., F.G.S. 



A recent journey to the National Park of the United States, 

 resulting in a study of the obsidians and rhyolites in the field and at 

 home, suggested a direct comparison between the hollow spherulites 

 characteristic of these rocks and those of the rhyolites of Shropshire, 

 Jersey, and elsewhere. 



The first part of the paper is concerned with the spherulites of 

 the Yellowstone region. A brief description is given (i) of the 

 small bluish-grey solid spherulites common in the obsidian of 

 Obsidian Cliff, and (ii) of a hollow variety in which radial structure 

 is barely discernible. In the latter, the spherulitic part is repre- 

 sented bj' a whitish, rather crumbly material consisting of felspar, 

 tridymite, and quartz. 



The hollow spherulites proper are divided into two groups — 

 (i) those containing cavities without definite form, and (ii) those in 

 which the cavities are related to the shape and structure of the 

 spherulite. The latter include the well-known lithoph3'see. The 

 manner in which these occur, and the relation of the cavities to 

 the enclosing spherulite, are described. Attention is drawn (a) to the 

 porous character of the latter, and (6) to the network of felspathic 

 fibres, studded with crystals of tridymite, which usually distinguish 

 the spherulite near a cavity. 



Hypotheses framed to account for these varying structures would 

 take one of two directions : — (i) Hollow spherulites are the result 

 of some property of the original magma, or (ii) are due to the 

 decomposition of an originally solid spherulite by heated waters. 

 Taking the second alternative first, a description is given of the 

 effect of solfataric action on the rhyolites of the Yellowstone Canon. 

 The conclusion reached is " that the action of hot waters charged 

 with silica may be to remove portions of the rock, or to permeate it 

 without destroying its characteristic structure ; that we obtain, 

 however, no evidence to show that the spherulites are most easily 

 attacked, but rather the reverse." Explanation, therefore, is most 

 naturally sought in some property of the original magma, and that 

 propounded by Professor Iddings appears the nearest in accord with 



