392 



deposits, and is generally supposed to be unconformable to them. It 

 is very soft when first exposed, but hardens by exposure to the atmo- 

 sphere ; and is occasionally marked by belts and nodules of white 

 sand, and in the lower part contains rounded fragments of granite, 

 quartz, and other older rocks. No organic remains have been no- 

 ticed in it. 



The upper red marl is exposed only at CoUyhurst, about a mile to 

 the north-east of the Manchester Exchange, in the old road to Blake- 

 ley; but it has there yielded a greater number of fossils than has been 

 found in any other bed of the superior divisions of the new red sand- 

 stone group in England. 



The deposit extends about a hundred yards, and at one of the 

 points examined presented the following details : 



Top a. Variegated marls, no organic remains .... 6 inches. 



h. Strong, red marl, traversed near its centre 



by a thin layer of fragile bivalve shells . . 5 



c. Light-coloured, calcareous marl, marked 



with lines and spots of a beautiful red . . 3 



cl. Light-coloured, calcareous, strong marl, 

 containing an immense number of imper- 

 fect casts of bivalves and perfect univalves 5 



When the marl is first excavated it crumbles 

 under the touch, but after exposure for a 

 short time, it is fractured with difficulty. 



e. Clay, striped red and white, and containing 



casts of bivalves 4 



/. Light-coloured marl, similar to No. 4, and 

 inclosing numerous casts of bivalves and 

 univalves 3 



g. Variegated marl, with an immense number 



of univalves and bivalves, 2 inches 2 



h. Indurated red marl, mottled with streaks of a 

 greenish colour. The upper part contains 

 numerous casts of large bivalves, and the 

 light-coloured streaks also inclose casts 

 of bivalves and univalves. Few shells are 

 found below the depth of one foot, though 

 the author had the bed penetrated to the 

 depth of 29 feet, when an influx of water 

 prevented them from boring any further. 

 The rhomboidal fracture, so characteristic 

 of the red marl, was very observable in 

 this bed ' 29 feet. 



With respect to the geological position of these fossiliferous marls, 

 the authors are fully satisfied that the deposit reposes on the upper 

 new red sandstone by which the marls are surrounded, though, from 

 the covered nature of the ground, the connexion of the two forma- 

 tions cannot be ascertained. In mineral aspect the lowest beds at 

 Collyhurst are said to agree with the upper red marl of Lincolnshire 



