124 Igneous Origin of some Trap Rocks. 
large veins just under the skin of an animal. This sandstone is not 
only argillaceous, but it is caleareous. Its numerous fissures are oe- 
cupied by thin veins of calcareous spar, generally not thicker than a 
goose quill, but occasionally swelling into larger dimensions, and some- 
times dying away in scarcely visible lines: crystals of cale-spar, some- 
times of tolerable regularity, are not very uncommon, and there can 
be little doubt that the entire rock would effervesce, but I did not 
happen to have any acid with me when I was there, by which I 
could make the trial. A very curious circumstance in this sandstone, 
is its constant disposition to split into huge rhomboidal tables. It al- 
ways has this figure marked out by regular fissures, as it lies in the 
quarry, and it comes out in this form, as may be seen abundantly in 
the pavements of the side walks and crossing places in Hartford. 
The appearance is too constant to justify the supposition that it was 
accidental ; it undoubtedly resulted from some law, but I would not 
venture to say that the rhomboidal figure had any connexion with a 
tendency to crystallization, produced by the carbonate of lime, which 
is contained in the rock.* 
The strata of this argillaceous sandstone are inclined, and dip to 
the S. E. at an angle of, apparently, from ten to fifteen degrees ; it 
contains some veins of sulphate of barytes, occasionally stained by 
green carbonate of copper, and united to crystallized quartz. 
trap rock is of the variety called greenstone ; it is, obviously 
to the eye, and still more distinctly to the magnifier, composed of 
hornblende} and felspar, and possibly quartz, aggregated in a con- 
fused and very compact crystallization. It is exceedingly firm, and if 
taken from the distance of four or five feet above the sandstone, it is 
very difficult to break. No person at all accustomed to chemical 
*Nor am I quite certain that the rhomboidal figure is common toa looser kind of 
sandstone which forms the greater part of that kind of stone found in the quarry, and 
which on being exposed for a year or two to the air, crumbles into pieces, presenting 
gillaceous. sandstone replete with clay, which has given the excellent basis that will 
8 vicinity, the fine soil which it now enjoys; and the coler, se 
strong as to have given origin to the application of it in paper printing, is owing to 
the oxide of iron, so abundant in this stone, 
$ Perhaps sometimes augite. . 
