108 
GEOLOGY OF THE SECOND DISTRICT. 
This rock is perfectly compact in its texture, and breaks with a smooth conchoidal frac¬ 
ture. The only crystalline particles, are those which occupy the space where an organic 
being was enclosed : thus, the fossil known as the Fucoides demissus, in many places is 
changed into slender sparry columns ; but as a whole, the rock is perfectly compact; and, as 
in most rocks which give this kind of fracture, it posseses a kind of brittleness, which, by a 
single smart blow, enables us to break off large fragments of the rock. As a limestone, it is 
perfectly pure, being free (with the exception I shall make) from silex or other earthy matter. 
It is susceptible of a good polish, and may be used extensively as a marble : the only objec¬ 
tion to it, arises from its brittleness, and liability to fracture in working. 
The birdseye contains several layers of a drab color, which may be found suitable for water 
lime, in all amounting to about ten feet in thickness. These layers present a strong contrast 
to the birdseye, being granular, and of a yellowish white ; while the former is blue or bluish 
grey, with a slight translucency. This rock is an excellent material for lime, forming proba¬ 
bly one of the purest of any in the class of limestone. The lime employed by the Redford 
Glass Company, is made from this rock. 
The fossils of this rock, though they appear in some localities quite numerous and charac¬ 
teristic, are yet very difficult to be obtained : they are either mineralized by calcareous spar, 
or else, in consequence of the compactness of the rock, and the peculiar fracture and little 
disposition to weather, it is exceedingly difficult to obtain them except in fragments. I have 
noticed, however, a peculiar species of Isotelus, an Orthocera, a Leptsena, and a large Cythe- 
rina. The fossil which is supposed to characterize the rock, is the Fucoides demissus of Con¬ 
rad. In relation to it, I take the opportunity to remark, that in consequence of having found 
some additional parts of it, it is evident that it is not a vegetable. It is true, that as usually 
presented in the rock, it appears like a fucoid; but in many places its structure is either de¬ 
stroyed by weathering, or by crystallization, and here its true character is not revealed. In 
other instances, it is beautifully exposed by weathering, the internal structure being finely 
displayed on the surface of those rocks which have weathered smoothly. In addition to this, 
I have discovered that the outside of the hanging stems are perforated like Polyparia; a 
fact which clearly indicates the true nature of the fossil, and the kingdom to which it be¬ 
longs. 
