206 PROF. BOSWELL ON THE CRETACEOUS AND [vol. lxxix, 



Oligocene (Aquitanian ). 1 



Petrockstow, near Torrington (Devon). 

 Bovey Tracey and Newton Abbot (Devon). 



Pliocene^ 2 



St. Erth and Lelant (Cornwall). 



Crouza Down, near St. Keverne (Cornwall). 



St. Agnes (Cornwall), 



together with certain deposits of doubtful age (see p. 223). 



The respective heights of the upper and lower surfaces of the 

 deposits above Ordnance-datum are as follows : — 



Upper Surface. Lower Surface. 3 



Cretaceous. Feet. Feet. 



Great Haldon 800 on N. to 600 on S. 750 on N. to 550 on S. 



Little Haldon 600 on N. to 700 on S. 550 on N. to 600 on S. 



Eocene. 



Marazion 20 to 30 ?0 



Buckland Brewer . approx. 260 200 3 



Great Haldon reaches 830 800 to 600 3 



Little Haldon reaches 810 600 to 700 3 



Oligocene. 



Petrockstow 300 ? less than 200 



Bovey never above 500 ? 100 or more below 



Ordnance-datum 



Pliocene. 



St. Erth P110 ?90 



Lelant 180 180 



Crouza Down 365 



St. Agnes. 350 to 420 ? 340 to 410 



II. Evidence of the Age of the Deposits. 



Good general descriptions of the various deposits have been given 

 by various authors (mentioned below), and, so far as field-evidence 

 is concerned, little can usefully be added to their accounts. 



The age of the Cretaceous deposits was determined as Upper 

 Greensand from their fauna, the zones recognized being those of 

 SchloenbacJiia rostrata and JPecten asper.^ The presence of 

 weathered and stained flints and of derived Chalk fossils (including 

 Mars up ites) in the beds of gravel capping the Haldon Hills, of 

 carious and weathered flints in the gravels near Bucldand Brewer, 



1 I have followed Clement Reid, in the Geological Survey Memoir (1913), 

 in grouping the Aquitanian with the Oligocene. It is now generally re- 

 ferred to the Miocene age. 



2 These deposits have been dealt with recently by Mr. H. B. Milner. Notes 

 on them are here inserted for completeness and for comparison. 



:i Owing to a certain amount of sagging on the slopes of the hills, the 

 difference between the levels of the upper and those of the lower surfaces 

 is often far greater than the actual thickness of the deposits. 



4 ' The Cretaceous Rocks of Britain : vol. i ' Mem. Geol. Surv. 1900, p. 218 ; 

 ' The Geology of the Country around Newton Abbot (Sheet 339) ' Mem. Geol. 

 Surv. 1913, p. 93 (hereafter referred to as the ' Newton Abbot Memoir '). 



