GEOLOGY 
them downward. Probably if we could have measured the rate at 
which these movements were progressing we should have found them 
almost imperceptible, even when the observation extended over centuries. 
At whatever rate the subsidence may have proceeded it continued through 
a sufficiently long period to allow of the accumulation of layer upon 
layer until a pile several thousands of feet in thickness was accumulated. 
At a late period in the history of these rocks there seems to be 
evidence that some upheaval took place, and there was laid down one or 
more bands of pebbles, of which bands, now hardened into conglomerate, 
we have now traces near Keswick, and also at Cockermouth and elsewhere. 
After that followed a period of somewhat deeper water conditions, during 
which finer mud subsided to the sea bottom here. It was chiefly during © 
this period that the animals lived of which fuller mention will be made 
presently. 
(6) The peculiar conditions under which these old sediments were 
deposited extended in one direction beyond where the Isle of Man is now, 
and, in the other, into north Cumberland. It is possible, however, that 
they did not extend much farther north. It may well prove some day 
that the earlier deposits of this age are contemporaneous with the upper 
part of the Durness Limestone of north-western Scotland. In this case 
there must have been deeper water conditions in that direction, and 
therefore, possibly, the old land from whose waste the Skiddaw Slates 
were derived may have lain to the south-east. Be that as it may, we can 
feel much more certain regarding the nature of the sea bottom, and the 
physical geography in general of the area adjoining the Solway during 
the latter part of the period when the Skiddaw Slate was being formed. 
We have records in the southern uplands of Scotland (the old Valentia 
of the Romans) of an important series of volcanic outbursts taking place 
on the ocean floor and apparently in deep water. There is no clear 
evidence that these volcanic conditions extended into the area where 
Keswick is now, although some volcanic rocks in the Caldbeck Fells 
may eventually prove to belong to this period. The conditions that 
obtained in what is now north Cumberland at this period may have 
borne a close resemblance to those now found on the eastern margin of 
the Indian Ocean, where volcanic rocks, rocks of oceanic types, and 
terrigenous deposits from the land are being laid down in close con- 
tiguity to each other, and sometimes change their relative places. 
Beneath what are now the Border Counties there lies buried at a 
great depth another phase of sedimentation, of which it is probable 
representatives may occur in Cumberland. We have good reason to 
believe that while the middle part of the Skiddaw Slates was being 
formed, the ocean floor in the northern part of the area sank to a vast 
depth, so that the sea bottom there at the period under consideration lay 
for a vast length of time at a depth of between two and three miles below 
sea level. The nature of the deposit that accumulated there is in all 
essential respects comparable with the Radiolarian Ooze which is being 
slowly formed in the greater ocean depths at the present day, especially 
3 
