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OF SOUTH CAROLINA. 45 
conglomerates, and sandstones, of a brick-red colour. In New York this system is best developed 
in the Cattskill group, where it rises into mountain peaks. In Pennsylvania and Virginia it is seen 
dipping under the conglomerates of the carboniferous system, but thins out towards the West. In 
Michigan it occupies a considerable space, and is found underlying the coal measures in the 
Western States. 
In England this system is well developed, and until a comparatively recent date it was thought 
to be a local deposit confined to that country. In Westmoreland and Herefordshire the Silurian 
rocks are seen passing into the Devonian rocks. In Scotland the system appears resting upon 
gneiss, the lower beds consisting of conglomerates of enormous thickness. It is here that these 
rocks have been studied with greatest care—a ground rendered classic by the genius of Miller. 
The Old Red Sandstone system of Russia bears a strong analogy to the English rocks of the 
same age, and many of the fossil shells are common to both. Previous to the study and correct 
determination of the British rocks, much difficulty was experienced in referring the Devonian 
system of Belgium and other parts of Europe to its place in the series; but its true position in 
England once settled, its peculiar fossils rendered the task less difficult elsewhere. The thickness 
of these rocks in America is at least ten thousand feet, but in Europe it is far greater. 
Corals were quite abundant during the period of the formation of the Old Red, and the molluses 
number some genera of higher organization than any that preceded them. 'The genus Clymenia 
seems to connect the Nautilus and Ammonite. On the other hand, the Trilobites, which were so 
abundant in the Silurian system, have disappeared so rapidly as to become quite rare. It is the 
remains of fishes, however, that afford the most striking characteristic of the system. Some of these 
Placoids, a family of cartilaginous fishes, the rest Ganoids. Some of them so singular and so unlike 
all the known forms of these animals as to require the genius of Agassiz for their determination 
and distribution in their proper place in the scale of creation. One of the most remarkable of these, 
the Cephalaspis, strangely reminds one of the common Limulus or King Crab, of our coast. The 
Pterichthys and Coccosteus were covered with beautiful and regular plates, forming a scaly armour 
of great strength. 'The Holoptychius was another of those strange fishes, found in the Old Red 
sandstone of Scotland, differing as much from all the rest as they did from the forms of the present 
day. Of fishes of this latter genus, Mr. Hall has figured the scales and a tooth in the Geological 
Report of the Fourth District. He has also figured, in the same Report, some bones, which he 
supposes the remains of a Saurian—the first of the type known in this system. 
Carboniferous System.—This system is composed of strata of limestone, of great thickness, 
called Mountain Limestone, and an immense group of rocks, composed of shale, coal, and sand- 
stone, which are found resting upon beds of conglomerates, and a white or gray sandstone, called 
mill-stone grit. The mountain iimestone, which is found at the base of the system, is very gene- 
rally, in this country, interstratified with beds of hornstone and cherty limestone; towards the top 
a stratum of magnesian limestone is found, and another bed of the same rock occurs near the base 
of the group, on the southern flank of the Cumberland Mountains. Prof. Troost has shown that 
the uppermost beds pass into an Oolite rock, on the mountains just named, and in St. Clair County, 
Alabama, similar beds occur, that are entirely silicious. The mountain limestone is extensively 
developed in the United States, being every where found underlying the coal measures. Dr. 
Troost estimates its thickness on the sides of the Cumberland Mountains at 200 he, oe 
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