12 THE GEOLOaY OF TYTHERTNGTON AND GEOVESEND. 



Feet. 

 Upper Limestones t . . • . t . 100 



/■Main portion 

 Middle Limestones ^ Mitcheldeania-heds > . . 1620 



'oolitic beds, 100 feet) 



Lower Limestones i ^^^^^ ^^^^' ^^^ ^'^^ ] 990 



(. Lower Limestone Shales, 500 feet ) 



Total .... 2710 



The Upper Limestones are the beds often spoken of as 

 Upper Limestone Shales, and described by Sir H. de la 

 Beche (Mem. Geol. Surv., vol. i., p. 129) as Upper Mixture 

 of Sandstones, Marls, and Limestones. Sir Henry gives the 

 thickness of these beds as 400 feet. But the boundaries of 

 these transition beds are always difficult to determine, and 

 this accounts for the discrepancy between the thickness of 

 these beds as given by him and that given by Prof. Hull, 

 which Mr. Wethered adopts. 



The oolitic beds are those seen in the old quarry at 

 the bottom of the gully. Concerning their position, Mr. 

 Wethered speaks with a somewhat uncertain note. On page 

 187 he writes : " At the top of the Black E-ock series there 

 is clear evidence of an alteration of conditions under which 

 the limestone was being deposited ; this is indicated by a 

 thickness of about 100 feet of oolitic limestone, which closed 

 what may be termed the 'Local Encrinite Period,' and 

 preceded conditions extending over a length of time difficult 

 to estimate, during which a great thickness of strata was 

 deposited in which crinoidal remains are few in number and 

 small in size." Here, therefore, he makes the oolitic beds 

 bring to a close the Lower Limestone series. But on the 

 table he gives (p. 189) he places the oolitic beds at the base 

 of the Middle Limestone. 



The Mitcheldeania-heds are those which I described in 

 these Proceedings (vol. iv., part 3) as Middle Limestone 



