128 



The section of Brent Knoll would therefore be the following*: — 



, r "Cephalopoda-bed" and ) 

 Midford Sands -^ ^, , [ about 200 feet 



( bands J 



Upper Lias ... Clay and Stone ... ,, 40 „ 



( Eock bed and Micaceous 1 



Middle Lias ) Sands / " " 



( Micaceous Shales and Clays „ 130 „ 



Hence the section published in the Geological Survey Memoir 



is incorrect, with respect to the Lower Lias, which may now be 



altered to Middle Lias. 



SECTION OF BRENT KNOLL. 

 Scale three inches to one mile. 



a. Cephalopoda bed. c. Upper Lias. e. Middle Lias Clays. 



b, Midford Sands. d. Mddle Lias Sands. 



Comparing Brent Knoll with Glastonbury Tor we find the 

 same structure with the exception that no traces of hard 

 beds at the top of the Midford Sands can there be recognized. 

 The Tor is formed of these Sands, resting on a platform of 

 Upper Lias Clay and Stone, beneath which come the Marlstone 

 rock-bed, and the Middle Lias Sands, well shown in some of the 

 deep road-cuttings. Micaceous clays and sandy Shales beneath 

 the Lliddle Lias Sands, are opened up in three brickyards to the 

 north-west of the Tor ; and although I could find no organic 

 remains in the beds I feel confident they belong to the same 

 division as the basement beds of Brent Knoll, which contain 

 Ammonites margaritaius. 



The general sequence of beds forming the Middle Lias of this 

 district is the following : — 



3. Marlstone rock-bed with A. spinatus, A. margaritatus, &c. 



* The estimates of the thickness of each division are based on the 

 height of Brent Knoll. 



