OF THE NEW RED SANDSTONE FORMATION OF PENNSYLVANIA. 
15 
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 the 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.”*— Lyell's Elementary 
Geology , 3 cl 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 may be 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 
Gasteropoda found in the brecciated Limestone rocks of both continents. The 
Thecodonts from Bristol are described, by Mr. King and by Professor Owen, ashavirg 
bi-concave vertebra, 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 vertebra, 
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 vertebra ; an analogous structure, but less 
marked, exists in the dorsal vertebra 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. 
■j* Transactions Geological Society, v. 3, N. S., p. 38. 
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