RICHARDSON : THE LOWER OOLITIC ROCKS OF YORKSHIRE. 199 
litholog}^ of the component divisions of the Scarborough Beds 
as they are followed round their outcrop — from the coast-sections 
at Gristhorpe to the inland quarries and scarps in the neighbour- 
hood of the Derwent Valley. Xo e\adence of any later deposit 
taking part in the formation of the Scarborough Beds than that 
of blagdeni hemera has yet been obtained. 
^Middle Estuarixes. — The stratigraphical position of these 
deposits is between the Scarborough and Millepore Beds. Like 
the Upper and Lower Estuarines they comprise beds of sandstone, 
sandy shales and thin coal-seams ; but their upper and lower 
limits are not always too well defined, there being a gradual passage 
into the sub- and super- jacent marine deposits both as regards 
faunal characters and lithic structure. 
At Gristhorpe Bay the Middle Estuarines are 40 to 50 feet 
thick ; at Cloughton and Blea W^'kes about twice as much ; in 
the Howardian Hills, where the^^ are more arenaceous (" Middle 
Sands of Cram Beck "— Hudleston), from 20 to 60 feet ; while 
in South-east Yorkshire, where clay participates with the sand in 
their composition, they total 20 feet or more. 
The Scarborough Beds are well developed to the north of a 
line joining Gristhorpe and Kirkham Abbej^, and therefore over 
that tract the approximate upper limit of the Middle Estuarines 
is fairly easy to determine. But in South-east Yorkshire, where 
the Scarborough Beds are not thus prominent the fixing of the 
upper limit is a matter of some difficulty. 
On the other hand, the lower limit is easiest fixed in the dis- 
trict to the south of a line drawn westwards from Gristhorpe to 
Kir by Knowle on the western escarpment, for over that tract 
the IVIiQepore Bed (or Whitwell or Cave Oolite) is prominently 
developed, Avhile it is absent — as an easily recognised bed — from 
over the extensive moorland that is drained by the River Esk and 
its numerous tributaries. 
Over the district referred to a coal-seam affords the readiest 
means of approximately locating the lower limit of the series. 
The Middle Estuarines are principally noteworthy for the 
occurrence in them of a very rich plant-bed, which rests immediate- 
ly on top of the bottom mass of sandstone at Gristhorpe Bay. This 
bed has jdelded innumerable plant -remains, specimens of which 
