20 
BLAKE : EAST YORKSHIRE. 
It is known, however, that intercalated amidst these 
estuarine beds are three well-known marine bands ; one, 
indeed, below them all, and therefore easily accounted for by 
the estuarine conditions not having set in. In addition to 
these, a fourth, well characterised, has recently been discovered 
by Mr. Borrow, of the Greological Survey, in the northern area. 
Nothing is more difficult, however, than to truly correlate 
these with all the intercalated limestones of the same series 
in the Howardian Hills. Thus we incidentally have proof of 
their local character. We may therefore explain them by 
minor changes within the district, some of which were 
favourable to the development of marine life, which left its 
relics as limestone rock. In some places, doubtless, coral 
reefs of small size were able to establish themselves. But the 
total result evidently was that the sea became so shallow that 
none of the rich material which elsewhere made the great 
limestones of the Great Oolite ever reached the district, and a 
period of slow deposition dragged on its weary length till 
fresh changes were brought about. 
Not one of these observations applies to the small patch 
of Oolitic and Upper Liassic rocks to the south of Market 
Weighton. There the Middle Lias is capped by beds of a 
more southern character, the Upper Lias has no jet, and the 
small patchy representatives of the Lower Oolites are as much 
or more marine than estuarine. Here then we have the 
farthest outskirt of a large area of deposition, showing in 
Lincolnshire its own peculiar features, but scarcely exhibiting 
them in this little corner of Yorkshire. These beds, however, 
are of great use as showing how isolated is the true Yorkshire 
basin, and how truly local are its deposits. 
This brings us to the close of the first chapter of the 
history. After the cornbrash was formed, which may be 
regarded, as merely another local limestone (there is none in 
South Yorkshire), to be accounted for as before, anew series of 
