28 
GEOLOGY OF THE FOURTH DISTRICT. 
and Virginia. It is an interesting rock, as exhibiting to us the dawn of animal life ; and the 
first living thing entombed and preserved through unnumbered ages, its delicate structure un¬ 
effaced to the present moment, is a species of Lingula, which is its only known fossil. This 
fact affords a remarkable example of the tenacity of life in this family of shells, for we find 
them in every successive group in the system ; they have existed in every geological era, and 
are living in the present ocean. 
2. Calciferous Sandrock. 
The Calciferous sandrock, a mass for the most part intermediate between sandstone and 
limestone, being an intermixture of both, forms the next rock in succession, and appears 
equally extensive. Indeed, in some places, it is more persistent than the former. It is a very 
important rock in the First, Second and Third districts, both in extent and thickness. It is 
likewise interesting from being the lowest position in which anthracite coal is known to exist, 
being found in this rock associated with the quartz crystals. It yields the finest quartz crys¬ 
tals known, and they are more or less abundant in all situations where the rock occurs. 
Organic Remains. — In nearly all the situations where this rock appears, fossils are rare or 
entirely wanting, and but few individuals have ever been found. Those at present known 
are the following: Lingula acuminata, Ophileta levata, 0. complanata, Pleurotomaria, Or- 
thoceras primigenius, and plates of Crinoidea. 
In the upper layers of this rock at Chazy, Dr. Emmons has obtained the following fossils : 
Scalites angulatus, Maclurea labiatus, M. striatus, Bellerophon sulcatinus, Orthis and Orbi- 
cula. 
There is also a layer characterized by the presence of fucoids, which is very persistent; 
and probably from these marine plants is derived the carbonaceous matter which forms the 
anthracite. 
3. Black-river Limestone Group. 
This group consisting of the Birdseye and Chazy limestone, is a remarkably persistent 
mass, being known together with the succeeding one, almost or perhaps the entire width of 
the continent. The rocks of this group appear in the northwestern part of New-York ; they 
extend thence into Canada, and they are seen on Lake Huron, upon the Mississipppi river, 
at Frankfort in Kentucky, and are well known in Pennsylvania and Virginia. 
Organic Remains. — The Birdseye limestone of Prof. Eaton forms a part of this group, 
being every where known by the presence of its peculiar fossil, the so called Fucoides demis- 
sus, (since ascertained to be a coral,) which is typical of this rock in all situations. Besides 
this fossil, it contains a species of trilobite, Orthoceras multicameratus, Ellipsolites ? Stro- 
phomena lsevis. Few others are known, and it usually appears destitute of such remains. 
The Chazy limestone, which is considered by Dr. Emmons a distinct rock, contains a few 
fossils peculiar to itself. These are the Maclurea, a fossil closely allied or identical to Euom- 
phalus ; Columnaria sulcata, with a few others. 
