On the Siluria7i System. \ 87 



characteristic fossil, the scales of a fish termed Holoptychus no- 

 bilissimus, figured in Murchison's work on the Sikirian system. 

 This rock not only holds precisely the same place between the 

 coal and the Silurian rocks, and contains the same characteristic 

 fossil, but is the same in color and mineral character, as the old 

 red sandstone of England. It occurs on the rail-road near Bloss- 

 burg, Tioga county, Pennsylvania, whence I received a fine speci- 

 men last spring. The carboniferous system is also well devel- 

 oped in this country, but the mountain limestone is rare and in 

 thin depositions generally. The fossils, however, are numerous 

 and well characterized in the shales and ironstone nodules. The 

 next succeeding formation or system, the new red sandstone, 

 is very limited, and above it we find no trace of that interesting 

 series of rock, the oolites, lias, wealden, &c., but the cretaceous 

 rocks are widely distributed. Finally, the tertiary formations, 

 corresponding to the eocene, and older and newer pliocene, stretch 

 along nearly the whole of the seaboard. I have lately ascertained 

 that the eocene or lower tertiary occurs in the bluff at Natchez, 

 Mississippi. The various formations, from the coal inclusive to 

 the top of the series, have been found to correspond with those 

 in Europe in a remarkable manner. It remains now to determine 

 how far the correspondence between the subdivisions of the Eng- 

 lish and American Silurian rocks can be determined. As I have 

 lately examined the splendid work of Murchison with this view, 

 it may be interesting to geologists to learn the result, although it 

 is necessarily as yet but an imperfect view of this important sub- 

 ject. Beginning, therefore, with the Llandeilo flags, I will ob- 

 serve that this formation in the New York geological reports was 

 compared to the Trenton limestone, but since the examination of 

 Murchison's work I find that the Llandeilo rocks are characteri- 

 zed by two species of trilobites which are extremely rare in this 

 country, and although they occur in the Trenton limestone, I 

 cannot but consider them as evidence that the Llandeilo rocks 

 have been thinly deposited and subsequently swept away. 



Caradoc Sandstone. 



This appears to correspond with the celebrated limestone of 

 Trenton Falls, known by the name of Trenton limestone, which 

 occurs in many places in the northeastern portion of New York 

 and in Canada, and passing under the upper Silurian rocks, reap- 



