224 



similar couclitions. This correspondence in time, its " Homotaxis," Avoukl 

 seem to imply that this extended area must have occuiTed or existed as 

 a shallow sea, in which the numerous vertebrate occupants have left to 

 us their scattered remains and testimony, and also that it was not by 

 currents or drifting, that these bones could have been carried and sorted 

 where they now occur, but were regularly deposited and bedded in the 

 position they now occujjy. I am thus induced to believe, from the 

 peculiar relations which exist between the organic remains and the 

 associated physical conditions, that this chief Bone bed was synchronously 

 deposited over the area it now occupies in the West and South-west of 

 England. The dying out or extinction of the species contained in, and 

 peculiar to the beds of this age, would indicate synchronous and similar 

 conditions of change in the relative positions of land and sea : and in the 

 case of the Bone bed, I am induced to beUeve that it was accumulated during 

 a period of slight elevation, as the sub-angular pebbles or nodules contained 

 in, and comprising much of the bed in some localities, is re-constructed 

 new Bed Marl; and especially is this the case at Aust Passage, where 

 the bed attains a thickness of about 9 inches, three-fourths of which is a 

 marly conglomerate. The Westbury bed, however, is chiefly and purely 

 Bone breccia, and is the richest in the remains of Saurians and Fish, 

 and their excrementitious matter, with which I am acqiiainted; although 

 at the northern extremity of the Aust or Old Passage section, where 

 mixed with the white and grey nodular marls, it attains the thickness, 

 as before stated, of 9 inches. The organic remains of this Bone bed are : — 



Acrodus minimus, Ag. Sargodon tomicus, Plien. 



Nemacanthus filifer, Ag. Plesiosaurus, vertebrae of 



monilifer, Ag. Ichthyosaurus, vertebrae and femur 



Hybodus minoi-, Ag. Pullastra arenicola, Strickl. 



pyramidalis, Ag. Axinus cloacinus, 0pp. 



Gp-olepis Albei-ti, Ag. Avicula contorta, Portl, 



tenuistriatus, Ag. Ceratodus. * 



Saurichthys apicalis, Ag. 



Succeeding this definite horizon are a series of dark brown shales, 

 about 7 feet in thickness. No. 10 in section, the upper half being darker 

 in colour than the lower, and weathers with a more rusty appearance. 

 This division between lower and tipper is determined by an indurated 



* I did not find the remains of Ceratodi here, although they abound at Aust. 

 Dr. Wright states in his sic loc. cit. that it occurs in the Bone bed at Westbury; I 

 therefore give it on his authority, which I do not doubt. 



