Vol. S9 .j 



TOAECIAN OF BEEDON HILL. 



455 



The interesting strata! feature, however, in comparison with 

 Dorset and the Co ttes wolds, is that here the Toarcian is thin 

 altogether ; it is not thick at the beginning and thin at the end, as 

 in the Cotteswolds, nor thin in the beginning and thick at the end, 

 as in Dorset. 



At another section near Caen, the Toarcian was much more 

 reduced. There was only about 8 inches of it, and that in pockets 

 in Caradoc Sandstone. It was limestone (and most of it crinoidal 

 limestone), resting on conglomeratic sandstone with crinoids, belong- 

 ing, on Dr. Brasil's authority, to the zone of Ammonites mar- 

 garitatus. The following is the sketch that I made : — 



Diagram of an exposure at May-sur-Orne (Calvados). July, 1895. 



Bradfordensis and Murchisonae, 4 feet 



ginches) Toarcian 



[The top of the striatulum-bed was eroded.] 



V. Cheonometby oe the Toaecian. 



In some districts — East Gloucestershire for instance — only a few 

 feet of Toarcian are found separating the Inferior Oolite (Aalenian) 

 from the Middle Lias (Pliensbachian). But what is the true time- 

 interval in such a case? In West Gloucestershire — the western slope 

 of the Cotteswolds — there were some 300 feet of strata laid down 

 during this time-interval. This is not, however, the full measure of 

 work accomplished : all but a few feet of these 300 belong to the early 

 part of the Toarcian Stage. The thin deposits of the later part of 

 the Toarcian Stage in the Cotteswolds give no true value for time- 

 measurement ; but a juster estimate can be obtained from the 

 thick deposits of the Dorset coast, which belong to the later part of 

 the Toarcian. So, in order to obtain a more correct estimate of the 

 amount of work accomplished in the way of deposition, it is necessary 

 to take the times during which the strata of the Toarcian Stage were 

 laid down, and see how much work was accomplished during each 

 one of them. The south-west counties of England yield the follow- 

 ing results, so far as investigations have yet proceeded : — 



