310 



THE GEOLOGIST. 



Througliout his paper he spoke of thein as "Lower South Devon, Lower 

 North Devon, Lower Cornwall, Upper North Devon, and Upper Cornvrall," 

 but stated that he applied the terms " Upper" and " Lower" to the rocks of 

 Devon and Cornwall as a matter of convenience merely, and not as embodying 

 or implying any opinion respecting the co-ordination of these rocks, with 

 deposits of the Devonian age elsewhere. 



Eighty-seven per cent, of the fossil species found in them are peculiar to one 

 or other of the five areas. Ranged in the order of their specific fossil wealth, 

 whether total or peculiar, they stand thus, in descending order : Lower South 

 Devon, Upper North Devon, Upper Cornwall, Lower Cornwall, and Lower 

 North Devon. There is a greater number of species common to Devonshire 

 and the Devonians of strata of continental Europe than to the five areas. If 

 the entire number of species found in the district under consideration, be put 

 as = one thousand, we have twenty-one derived from the Silurian, eight hun- 

 dred and six peculiar to the Devonian, and one hundred and seventy-three 

 which passed over to the Carboniferous age. 



The latter part of the paper was occupied with the discussion of various 

 hypotheses respecting the cause of the peculiarities of distribution which had 

 been described. 



ON THE AVICULA CONTORTA BEDS, AND LOWER LIAS OF THE 

 SOUTH OF ENGLAND. 



By De. Thomas Weight, F.R.S,E., F.G.S. 



The object of this paper was to show that the beds known as the "black 

 shales with the bone-bed" which rest upon the grey marls of the Keuper con- 

 tained a fauna which was special to them, and that many of the species were 

 identical wdth those found in the Upper St. Cassian beds of Germany, and the 

 Kassen strata of the Tyrol. Dr. Wright described detailed sections of the 

 " Avicula cortorta beds" at Garden Cliif, near Westbury-on-Severn, which he 

 considered as the best type in England, at Wainlode cliff on t]ie Severn, at 

 Aust cliff on the Severn, at Penarth near Cardiff, and at Watchet near St. 

 Quartock's head, the railway cuttings at Uphill and Saltford, and sections of 

 tlie same beds at Binton and Wilmcote, in Warwickshire, were described. 

 Nearly the same physical conditions prevailed in the deposition of all these 

 beds. The fauna was limited as to the number of species, but abundant as to 

 individuals. Fedeii Valoniensis (Befr.), Acicida contoda (Forfl.), Cardium 

 ,-li('lici',!i (Mor.), Pollastra arenicola (St rick.), Avere found in nearly all tliese 

 beds. The " bone-bed" was likewise well exposed in many of these localities. 

 Tlic fishes of the "bone-bed" had long ago been referred by Prof. Agassiz, Sir 

 Pliili]) Egorton, to species which were found m the Trias, and the ]\iolluscous 

 fauna, as far as it was knoAvn in England, was special to this zone, for these 

 reasons many geologists consider the " Avicula contorta beds" as the upper 

 fossil ilVrous portion of the Trias rather than as the basement beds of the Lias, 

 The qiicsl ion was an interesting one, inasmuch as fossil mammalian teeth of 

 Mici'olcstes hntl Ijcen I'onnd in the "bone-bed" of Germany many years ago, and 

 recently Mr. ^iloore had discovered them in a deposit of the same age near 

 Kronie. 



The Ijowcr Lias may be divided into six zones by the ammonites contained 

 in each of these snh-divisions ; tiic lowest, No. 1, contains Ammodites plcuiorUs 

 (Sow.) in great al)iin(l;inee ; this zone is well exposed at Street, in Somerset- 

 shirr, at Up Lyme, near Lyme llegis, at Watchet and Penarth, and in War- 

 wiekshii-c and Glouccstershii'e in several loccilities, all the fine Enaliosauiian 



