PROCEEDINGS 1849 — 1858. 
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westward to near Thirsk. They are composed of Calcareous Grit or 
Coralline Oolite at the top, with Oxford Clay, or some of the softer 
rocks of the oolitic series beneath. Their formation is traceable to this 
structure, and it has been considered that the valleys were produced 
in all probability by the action of streams now running in them, but 
Dr. Sorby, after a careful consideration, especially of Yedmandale, 
considered that the phenomena appeared to indicate that they had 
been washed out by the sea when the land was at a lower level than 
at the present time, by a current from the north. The larger expan- 
sion of the upper part of the valley appears to be better accounted 
for by this supposition than any other. The excavation took place 
previously to the time when the chief part of the erratic drift 
was deposited. He appears to consider that the drift occupying the 
lower level was beneath the water, whilst the higher parts of the land 
were above the sea. 
In June, 1851, he communicated the result of investigations on 
the microscopical structure of the Calcareous Grit of the Yorkshire 
Coast. Good sections of this grit may be seen at Filey, Gristhorpe, 
and Scarborough. The greater part of it is a sandstone containing 
a variable quantity of calcareous matter, but a considerable portion 
contains a great deal, and is much hardened by the infiltration of 
agate, which has solidified many of the shells and the wood, and filled 
the chambers of many of the ammonites. It is to this part of the bed 
that the author calls attention. If the calcareous grit be dissolved in 
hydrochloric acid there remains portions of agatised shells and a quantity 
of sandy matter. When this is examined under the microscope it is 
found to contain a very large quantity of reniform bodies, which are 
evidently not sand but some kind of of minute organisms converted 
into agate. These reniform bodies have a structure similar to that 
frequently seen in large agates, the deposit having begun from the 
sides and left a vacancy in the centre, which was afterwards filled up 
with less pure agate in alternating layers. He counted in a space of 
1 -280th of a square inch no less than forty of these bodies ; there- 
fore, there are on a square inch 11,200, and since they are on an 
average 1 -200th of an inch in diameter, there would be about two 
and a half million in one cubic inch. These small bodies differ 
