124 Igneous Origin of some Trap Rocks. 



large veins just under the skin of an animal. Tliis sandstone is not 

 only argillaceous, but it is calcareous. Its numerous fissures are oc- 

 cupied by thin veins of calcareous spar, generally not thicker than a 

 goose quill, but occasionally swelling into larger dimensions, and some- 

 limes dying away in scarcely visible lines : crystals of calc-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 w^ith me when I v/as 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 hes 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 jusdfy 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 tiie 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. 



The trap rock is of the variety called greenstone ; it is, obviously 

 to the eye, and still more distinctly to the magnifier, composed of 

 hornblendef 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 tiae rhomboidal figure is common to a looser kind of 

 sandstone which forms the greater part of that kind of stone found in the quarry, and 

 Avhich on being exposed for a year or two to the air, crumbles into pieces, presenting 

 an appearance like that produced by the slacking of lime. This kind of stone is reject*- 

 ed or used to make roads and paths, or for rough work, and only that which is in 

 rhomboidal tables is carried into Hartford for pavements. The strata of this are con- 

 tinuous for a great extent in the quarry; a particular stratum being found regularly 

 at a particular depth through the whole quarry. It is the decomposition of this ar- 

 gillaceous sandstone replete with clay, which has given the excellent basis that will 

 always insure to this vicinity, the fine soil which it now enjoys; and the color, so 

 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, 



t Perhaps sometimes augite. 



