246 G. L. Elles §• E. M. R. Wood— On the Drygill Shales. 



it can never have had the chance of becoming sufficiently cool to 

 solidify. If this be the true statement of the case, no reliable 

 estimate of the age of the world, based on considerations of the 

 present temperature gradient at the surface, has hitherto been made. 

 If the interior be liquid, and the central parts have been constantly 

 receiving greater accessions of heat than the parts more distant from 

 the centre, convection-currents must have been set up, and must 

 have played the chief part in the secular cooling. The age of the 

 world would therefore be dependent upon the degree of their activity, 

 which is not known. Another important consequence would follow, 

 because the currents would necessarily have a horizontal flow in the 

 parts of their course where the liquid had ceased to rise and had 

 not yet begun to descend ; and this would produce a horizontal 

 stress on the superincumbent crust, acting more powerfully upon 

 it at those places where the bottom was most uneven, as beneath 

 mountains. Thus we should be able to account for one cause, at 

 least, of the compressing force for which geologists are in search. 



WOODWAKDIAN MuSEUM NoTES. 



in. — Supplementary Notes on the Drygill Shales. 

 By G. L. Elles and E. M. E. Wood, Newnham College, Cambridge. 



IN the Geological Magazine, 1887, Professor Nicholson and Mr. 

 Marr drew attention to a group of fossiliferous shales detected 

 in connection with the Borrowdale Volcanic Series. 



At the request of Mr. Marr, we undertook the examination of 

 larger collections of fossils made from the same locality, and the 

 object of the following notes is to place these on record, and, in 

 the light of further palseontological evidence, to assign to the beds 

 a more definite horizon. 



As Professor Nicholson and Mr. Mai'r showed, these beds occur on 

 the north side of a great mass of Skiddaw Slates in what has been 

 termed the Caldbeck Fells area. The shales to which we wish to 

 direct attention are situated north of the intrusive masses of Carrock 

 Pike and Great Lingy, and are of interest as lying between the 

 Skiddaw Slates on the one hand, and the Volcanic Series of Caldbeck 

 Fells on the other. They occupy the summit of the A-alley between 

 High Pike and Carrock Pike, and are exposed in Drygill, whence 

 Professor Nicholson and Mr. Marr have given to them the name 

 of the Drygill Shales. 



The following section is described by them in Drygill in descend- 

 ing order : — 



1. Drab-coloured shales, iinfossiliferous. 



2. Blue-grey shales, weathering white. 



3. Dark blue-grey or black mudstones. 



4. Volcanic rocks. 



5. Dark fossiliferous mudstones with Trilobites and Brachiopods. 



The general dip of the beds is to the S.S.W., and the beds of the 

 south fork of Drygill are probably the same as those exposed in the 

 highest part of the main gill, since the faunas are almost identical, 



