18 
BLAKE I EAST YORKSHIRE. 
the whole of the Liassic area of Great Britain ; but the sedi- 
ment came from different sources. In the North Yorkshire 
area, or, as we may call it, the Yorkshire basin, we miss the fine 
clays and the smooth intercalated limestones which, occurring 
so frequently at the base in other districts, have obtained for 
the formation its name ; and in their place we find rubbly, 
coarse, calcareous, clayey beds, with oyster and cardinia bands. 
These are succeeded by clays and thin ironstones; giving 
place, in their turn, to sandstones, with a new series of oyster 
bands ; and these, again, were covered with the calcareous 
rocks which are now ironstones. Above these come the clays 
of the Upper Lias, to complete the deposits of that epoch. 
Almost all of these beds below the last show a remark- 
able thinning out as we go east or south from Redcar, to 
come to a minimum in the centre of the basin. These pheno- 
mena point to a local source for the sediment. Probably 
throughout the whole of England the Lias clays are derived 
from the denudation of the coal measures; and the local 
characteristics of the former may be more or less due to the 
neighbouring features of the latter, when not disturbed by 
the intermixing of streams from many sources and the 
spreading out their deposits over large areas. But in the 
case of the Yorkshire basin we seem able to trace this more 
exactly, and to see the beds of the Lias following in inverse 
order those of the carboniferous series. 
The great upheaval which separated the Yorkshire from 
the Durham coal field must have left a vast anticlinal area of 
coal measures in a state peculiarly fitted to be acted on by 
denuding agencies ; and thus from its debris, not carried far, 
and therefore not very fine, the earlier Liassic beds were 
formed — at first, ifc may be, contaminated by Permian lime- 
stone or other extraneous matter ; till at last the rain and 
rivers, settling down to their main work of consuming the 
coal measures proper, were enabled to reproduce them in the 
