OF THE NORTH-WEST OF ENGLAND. 227 



The above-named beds, marked with asterisks, contain the 

 fossil shells described by Captain Thomas Brown in my 

 paper published in the first volume of the Transactions of the 

 Manchester Geological Society. Professor King, in his 

 elaborate Monograph on the Permian fossils of England, has 

 since described the following, collected by me from the cutting 

 at Newtown, namely: — Bivalves, Schizodns ohscurus, S, 

 rotundatus, Bakevellia antiqua, B. tumida and Pleuro- 

 phorus costotus. Univalves, Turbo Mancuniensis, T. 

 helicinus, Rissoa obtusaj R. Leighi, R, Gibsoni, tuid 

 Natica minima. 



Our late venerable president, Dr. Dalton, at p. 154, vol v. 

 (new series) of the Society's Memoirs, examined a portion of 

 the thin bed of limestone. He calls it Tinker's Brow lime- 

 stone, and states its specific gravity at 2.55, and proceeds as 

 follows : " There is some limestone found at Tinker's Brow 

 which may be supposed an edge of the Ardwick stratum.* 

 The analysis of this specimen shows it to be a compound or 

 mixture of carbonate of lime and clay. The two earths of 

 lime and clay are nearly in atomic proportions ; but this may 

 be merely accidental. The lime only is combined with car- 

 bonic acid. It contains rather more than the Ardwick stone. 

 Exclusive of iron, I found the compound to be nearly — 



Clay ., 36 



Lime 36 



Carbonic acid 28 



100" 



The lower part of the marls appears to pass into the under- 

 lying conglomerate, and no difference in the amount or direc- 

 tion of the dip can be detected. Although such last-named 



* The Ardwick limestone and the one at Newtown or CoUyhurst were long 

 confounded together as magnesian limestone, but it is now well known that the 

 former is a portion of the upper coal field, and the latter is a true permian 

 deposit. 



