RICHARDSON : THE LOWER OOLITIC ROCKS OF YORKSHIRE. 197 
membered ossicles of isocrinoids. Where this Crinoid-Grit is 
thick on the Eston outlier, the underlying limestone of division 
c is thin — so thin as to have led the late C. Fox-Strangways to 
remark, " it is very doubtful if any limestone exists below this grit." 
Coming now to the western half of the main upland mass tliat 
is situated to the south of a line drawn east and west along the 
valley of the Esk, the limestone-division is continuous westwards, 
but attenuates where the Crinoid-Grit thickens. In places the 
reduced thickness of the Umestone is probably due to dissolution 
by carbonated waters that have percolated through the porous 
overlying Crinoid-Grit. In the neighbourhood of Snaper House 
(on Collis Ridge on Helmsley Moor) the blue limestones of division 
c have been extensively worked for road-metal and must be at 
least 10 feet thick. 
The Crinoid-Grit, often replete, as on Osmotherley Moor, with 
isocrinoid remains, is well-dev^eloped in this western tract, ^ 
increasing in thickness towards the north in the direction of the 
Eston outlier at the expense — as already noted — of the underlying 
limestone. 
In this western tract several changes take place in the com- 
position of the shal}" division of the Scarborough Beds. At 
Spindle Thorn, on Spaunton Moor, a noticeable 5-foot bed of very 
hard blue limestone makes its appearance in the lower part, and 
may conveniently be called the " Spindle-Thorn Limestone." In 
the upper part of this same shale-division a thick fossiliferous grit 
becomes prominent and forms great spreads, often more than a 
square mile in extent on the ridges and watersheds that separate 
the various dales. As it is most conveniently studied in the 
neighbourhood of Lambfold Hill, the term " Lambfold-Hill Grit " 
may not be inappropriate wherewith to designate it. 
In Bogmire Gill, at the south-eastern termination of Collis 
Ridge, the following succession may be discerned : — 
and on the west side of Bilsdale, the next dale to the west, the total 
thickness of the Scarborough Beds cannot be far short of 70 feet. 
(a) f Shales 
20 feet -J- 
a few feet 
10 feet 
Scarborough 
Beds. 
\ Spindle -Thorn Limestone 
(6) Crinoid-Grit 
(c) Limestone, blue. 
I It is at least 40 feet thick on the watershed between Scugdale and Raisdale in the tract west 
of Bilsdale. 
