364 Geological Society : — 



Holothurians and Tunicata {e.g. Leptoclinum tenuet) have been 

 detected. 



The list of the Mollusca showed the range of each species in 

 Miocene and Pliocene beds and in the present seas. The authors 

 considered that the fossils agree in age with the middle or lower 

 portion of the Red Crag, but that whilst many species having a 

 southern character are present at St. Erth, and wanting in the 

 Crags of the east coast, the Boreal and Arctic forms found so 

 abundantly in the Crag are absent at St. Erth. 



In explanation of this remarkable fact, it is suggested that when 

 the St. Erth beds were deposited, although the North-Sea area 

 was in direct communication with the Arctic Ocean, the western 

 part of the British Channel was not, that the British Isles were 

 joined to the continent of Europe on one side and to Greenland on 

 the other, the Shetland and Faroe Islands and Iceland being the 

 remnants of the barrier that formerly divided the Atlantic from the 

 Arctic Sea. Evidence is given in support of this view from the 

 present submarine configuration of the North Atlantic. It was also 

 shown to be probable that the St. Erth area, in Pliocene times, was 

 more directly connected with the Mediterranean than at present, 

 by a marine channel tbat traversed France. 



March 10.— Prof. J. W. Judd, F.R.S., President, 

 in the Chair. 



The following communications were read : — 



1. "On the Alteration of coarsely spherulitic Pocks." By Gren- 

 ville A. J. Cole, Esq., F.G.S. 



The author stated that the pitchstone of Zwickau, Saxony, con- 

 tains large spherulites, remarked on by Cotta in 1847, which 

 are devoid of radial structure, and are traversed by the fine lines 

 of flow that characterize the glassy matrix. The centre of each 

 of these has been hollowed out by decomposition along cracks, 

 as may be seen at the ends of the branches into which the 

 cavity divides, and infiltration of chalcedony and caleite has 

 occurred. The lines of flow correspond on opposite sides of this 

 secondary mass, and do not bend round as if the spherule had 

 formed about some calcareous inclusion or about a vesicle. Similar 

 excavation and infiltration have occurred extensively among the 

 coarsely spherulitic layers of the Precambrian rhyolites of Lea 

 Pock, Wrekin, and in these the cracks traversing the rock are 

 seen, under the microscope, as mere lines when passing through 

 the matrix, but widen out at once, probably through more ready 

 decomposition along their walls, when they enter spherulitic 

 matter. In the white rock (Silurian rhyolite) of Digoed, near Pen- 

 machno, N. Wales, similar alteration has converted the closely set 

 spherulites (often three inches in diameter) into mere shells filled 

 with quartz and chlorite ; while a black slate-like decomposition- 

 product, with a hardness of 2-5 and a specific gravity of 2*77, occurs 

 occasionally here, and very frequently in the less coarse but similar 



