OF THE NEW RED SANDSTONE FORMATION OF PENNSYLVANIA. 197 



Mr. Lyell finds great difficulty in pointing out the derivative rocks of this forma- 

 tion. He says : 



"The brecciated limestone (No. 2,) contains no fragments of foreign rocks, but 

 seems composed of the breaking-up of the Permian limestone itself, about the time of 

 its consolidation. Some of the angular masses in Tynemouth Cliff are two feet in 

 diameter. This breccia is considered by Professor Sedgwick as one of the forms of 

 the preceding limestone, (No. 1,) rather than as regularly underlying it. The frag- 

 ments are angular, and never water-worn, and appear to have been re-cemented on 

 the spot where they were found. It is therefore suggested, that they have been due 

 to those internal movements of the mass which produced tlie concretionary structure; 

 but the subject is very obscure, and after studying the phenomenon in the Marston 

 Rocks, on the coast of Durham, I found it impossible to form any positive opinion on 

 the subject. The well-known brecciated limestones of the Pyrenees appeared to me 

 to present the nearest analogy, but on a much smaller scale."* — LyeWs Elementary 

 Geology, 3d ed., p. 302. 



Prof. Sedgwickf views these deposits (all of the Trias and Permian) as being of 

 violent mechanical origin, but having several characters in common, which enable us 

 to connect them together, and, for general purposes of comparison, to regard them as 

 one group. " The greatest difficulty in classing distant portions of the New Red Sand- 

 stones have not, however, so much arisen out of its mechanical origin and complexity 

 of structure, as from its general want of conformity to all the inferior formations." 



The inducements which lead me to lean towards the opinion that this calcarious 

 conglomerate maybe on the same horizon with the Magnesian Limestone of England, 

 are in the lithological characters, in addition to the organic remains of the Magnesian 

 Limestone. In the cabinet of our Academy we have a collection from Bristol, 

 England, some of the specimens of which are so similar, in their brecciated form and 

 in their colors, to some specimens I procured near Reading, as to defy a separation of 

 the specimens if placed together. But the much more important characters consist 

 in the similarity of the structure of the bones, together with the single small 

 Gasteropod, found in the brecciated Limestone rocks of both continents. The 

 Thecodonts from Bristol are described, by Mr. King and by Professor Owen, as havirg 

 bi-concave vertebrae, with the middle of the body more constricted, and the terminal 

 articular cavities rather deeper than in Teleosaurus ; and Mr. King says that they are 

 "chiefly remarkable for the depth of the spinal canal at the middle of each vertebrre, 

 where it sinks into the substance of the centrum. Thus, the canal is wider vertically 

 at the middle than at the two ends of the vertebrae ; an analogous structure, but less 

 marked, exists in the dorsal vertebrae of the Rhynchosaurus from the New Red 



* Murchison & Strickland detected in Shropshire a band of Limestone in the red sandstone, but no organic 

 remains. Proceedings Geological Society, v. 2, p. 563: 

 t Transactions Geological Society, v. 3, N. S., p. 38. 



50 



