444 COLE : DESCRIPTION OF PHOTOGRAPH OF BOULDER CLAY CLIFFS. 
up old bays of the sea, and land valleys debouching on the shore. 
The Geological Surface maps show its extension in Yorkshire so that 
there is no occasion to enter into detail. These maps bring out 
prominently, however, the facts that there were two sources of 
supply, — 1, glaciers descending from the Pennine Range into the 
Vale of York ; and 2, a great glacier impinging on the Yorkshire 
Coast, laden partly with Scandinavian boulders ; also, that the Moor- 
land Dales, south of the anticlinal from Burton Head to Robin Hood's 
Bay, as well as a large portion of the Wolds, were islands in a sea of 
ice. The glaciers swept round them on all sides, but not over them. 
As regards Filey Bay the effect of the ice pressing on the land 
in its course southwards was to pile up masses of Boulder Clay and 
morainic sands and gravel, so as to completely block up the end of 
the Vale of Pickering, and to alter its drainage, e.g. the River Rye, 
which used to flow into the sea near Filey, now passes through a 
modern gorge at Mai ton to the Vale of York. So thick was the ice 
that moraines were deposited at Speeton, and further along on the 
very top of the chalk cliffs, containing numerous large boulders of 
whinstone from Upper Teesdale, granite from Shap, together with 
various other rocks, such as quartz, Mountain Limestone, Lias, mica 
schist, &c, and even porphyry from Christiania. 
In attempting to ascertain the age of the Boulder Clay of Carr 
Naze several difficulties present themselves. In the first place the 
cause of the Ice Age itself is not a matter of general agreement, 
some geologists attributing it to astronomical changes, others to geo- 
graphical. Again, there are distinct evidences of several Boulder 
Clays, lying one upon another, with different characteristics, especially 
in Holderness, such as the Basement Clay, with arctic shells, the 
Purple Clay, and the later Hessle Clay. Recent investigations 
(Geol. Soc, 1895), have re-established the theory that there were 
inter-glacial periods in the Ice Age, which facilitated the decay of 
the glaciers during years of comparatively warm temperature. But, 
to all appearance, the Boulder Clay cliff of the section is homogeneous 
throughout,* and. as it rests upon the original Oolitic rock, it must 
* Unless a line of stratified sand about half-way up the cliff marks a 
possible division. 
