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mations pre-eminently characterized by their organic contents being 
three times the nmnber of those ilkistrated in the Silurian system." 
Caradoc sandstone. 
The organic contents of the Caradoc sandstone and Trenton lime- 
stone correspond as groups, and the Llandeilo flags are absent. The 
fossils common to the two groups are embraced in the following list : 
Trilohites. 
Cryptolithus tessellatus, 'Green^ (Trinucleus carractaci, Murch.) Ca- 
lymene punctata, Wahl, 
Shells. 
Strophomena sericea,(Leptagna, »SoM;.)Strophomena alternata,(Orthis, 
Sow.) S. compressa, (Orthis, Soio.) Orthis callactis, O. flabellulum, 
O. testudinaria, Delthyris tripartita? (Terebratula, Soiv.) Lingula at- 
tenuata, Trochus lenticularis, Euomphalus corndensis, (Louisville, Ken- 
tucky,) Bellerophon bilobatus, (abundant at Trenton Falls.) 
Thus we have thirteen species in the Trenton limestone, which are 
characteristic of the Caradoc sandstone ; thus identifying the formations 
notwithstanding the great difference in mineral composition. 
Salmon 7^iver sandstones and shales. By this name I have indicated 
a formation which over-lies and immediately succeeds the Trenton lime- 
stone series, and was the first to shew that it possessed a distinct group 
of fossil very different from those above or below it, I find not one of 
these species noticed in Murchison's work, and therefore the formation 
is probably wanting in Wales, 
Niagara sandstone. This name I applied to the red sandstone of Ni- 
agara and Oswego, and ascertained that its fossil remains are peculiar 
to it ; the splendid Fucoides Harlani characterising it in New-York, 
Pennsylvania and Virginia. Though this fossil has not been found in 
Wales, yet a shell which is peculiar to the Niagara sandstone, Bellero- 
phon trilobatus, (Sowerby,) occurs in the Caradoc sandstone, and in the 
strata above it we find Tentaculites annulatus, Agnostus latus, (A. pisi- 
formis, Murch, pi. 3, fig. 17,) and particularly the Pentamerus oblongus, 
and P. laevis which characterize the upper part of the Caradoc sandstone 
in Wales. Therefore, I presume that from the limestone containing the 
Pentamerus to the base of the Trenton series, all the rocks would be 
[Assembly, No, 50,1 26 
