344 
FOX-STRANCaVAYS : FILEY BAY AND BRIGG. 
After a time, probably from the gradual filling-up of this sea, 
sandy beds were again dejDOsited, and the conditions became more 
favourable for the propagation of a marine fauna which throughout 
most of the higher rocks becomes tolerably abundant. 
This was succeeded by a long interval of time, during which 
a great thickness of Upper Jurassic clays. Cretaceous, and possibly 
other rocks were formed. In course of time these were elevated 
above the sea and suffered extensive denudation, having been 
entirely removed from the area north of Filey before the commence- 
ment of the other great period we have evidence of in these 
sections. 
As to the origin and age of the Boulder Clay there is consider- 
able difference of opinion amongst geologists, but it is more generally 
conceded that it is the product of land ice in some form or other. 
Boulder Clay and other glacial deposits are found in considerable 
thickness all along the coast and down the great central valley of 
the county, while the interior moorland hills between are entirely 
free from any beds of this nature. It is therefore clear that these 
hills must have stood up above the sea of ice that surrounded them. 
From an examination of the stones included in the clay it is 
generally admitted that a large portion of the clay found in the 
Yale of York came from the western moorlands, while that of the 
coast is mainly derived from Scandinavia. The great ice-sheet 
which produced this clay must have ground against the coast with 
prodigious force, tearing up the large masses of shale that have been 
found at certain points, and piling up the ridges of sand and gravel 
that occur on the summit of the hills at Speeton and Irton, 600 ft. 
above the present level of the sea. By this means the drainage of 
the country was completely altered, all the streams flowing to the 
east being entirely dammed up and forced to cut for themselves new 
passages, as is so strikingly exemplified by the Derwent at Ayton 
and Mai ton. 
On looking at these photographs it is interesting to notice the 
great variations in climate that have taken place during the 
formation of the rocks, showing temperatures ranging from the 
almost tropical seas that produced the corals in the limestone to the 
