Vice-President’s Address. 299 
of the unconformities in Britain, vast and otherwise 
important as they undoubtedly are. Biologists taking 
note of the many and important changes in life that 
took place during the Devonian Period will probably all 
agree that this interval, vast as it seems, is yet not more 
than sufficient to account for the biological phenomena 
observed. 
Silurian (Salopian) Rocks —In the English Lake District 
the Salopian Rocks, stated in ascending order, consist of (1) 
a conglomerate lying in places unconformably upon the 
Ordovician Rocks; (2) Graptolitic Mudstone, which, although 
rarely exceeding 50 feet in thickness, yet shows by both 
its lithological character and the organic changes recorded 
by its fossils, that its deposition must represent an interval 
of time of enormous length. This is almost certainly a 
deep-sea deposit, one probably formed on the very outer 
verge of the zone of terrigenous deposits of its time. Above 
this lies the Pale Slates, a rock whose lithological character 
also suggests that it had a deep-sea origin, and therefore 
that it also accumulated at a very slow rate. The aggregate 
thickness of these two is rarely more than 600 feet. 
Judging by the organic changes which took place in the 
interval between the commencement of the Graptolitic 
Mudstones and the close of the formation of the Pale Slates, 
the time implied must far exceed that required for the 
formation of the 12,000 feet of terrigenous deposits which 
make up (No. 3) the remainder of the Salopian Rocks of 
Westmorland. 
About one-third of No. 5 consists of fine-grained grey- 
wackes, which contain a high percentage of quartz particles, 
and which, therefore, have probably been laid down as a 
fringe not very far from the margin of the old land, and, 
in consequence, at a comparatively rapid rate. The remain- 
ing two-thirds are of a more argillaceous character. Perhaps 
it would be safe to regard these rocks as consisting of two- 
thirds of rocks which were originally loams, and one-third 
which may be regarded as clays. The whole, of course, is 
of marine origin. From top to bottom this vast pile of rocks 
shows evidence of quiet deposition—a view of their mode 
