126 



bed," which occurs at the top of the Midford Sands in Glouces- 

 tershire. So far as the divisions of the Lias were concerned, 

 the identification of Upper Lias was satisfactorily proved by the 

 presence of Ammonites communis, A. hifrons, &c., on the platform 

 beneath the Knoll. Here pale earthy and rubbly limestones, 

 (beds which characterize the lower part of the Upper Lias at 

 Pennard Hill, and further south at Yeovil and Ilminster), are 

 turned up in the ploughed fields and may be traced on the brow 

 of the hill to the west of the Knoll. 



The Marlstone rock-bed was probably present in an attenuated 

 form, although at the time of my first visit I found only " one 

 loose block on the hill which might be identified with this bed." 

 At Pennard Hill its thickness is from 15 to 18 inches, and at 

 Glastonbury Tor it is not much more.* 



The rarity of sections, however, rendered the interpretation of 

 the Geology of Brent Knoll far from satisfactory, and I was 

 glad to have the opportunity of revisiting it in July, 1885, on 

 which occasion I had the advantage of being accompanied by 

 Mr. Alfred Gillett, of Street; Mr. J. Edmimd Clark, and Mr 

 Martin F. Woodward. 



On approaching the foot of the hill from the Brent Knoll 

 railway station, our attention was attracted by a spoil heap 

 thrown up from a well-sinking. This proved to consist of blue 

 micaceous Shale, and a search disclosed several specimens of 

 Amiiwnites margmitatus, together with BeUmnites and fragments 

 of lignite. 



This discovery leads to the conclusion that no Lower Lias is 

 exposed at Brent Knoll, for the well was commenced but a few 

 feet above the level of the Alluvium which encircles the hill» 

 and it had been sunk to a depth of 15 or 20 feet, if not more. 



* The thickness of "about 15 feet" assigned to the "Marlstone- 

 rock," at Glastonbury Tor, by Dr. Wright, is I feel sure much 

 exaggerated. See Quart. Jown. Geol. Sec, vol. xvi., p. 34. 



