Open main menu

Page:Notes on the State of Virginia (1853).djvu/45

This page has been proofread, but needs to be validated.

from the horizon towards a parallelism with the axis of the earth. Being struck with this observation, I made, with a quadrant, a great number of trials on the angles of their declination, and found them to vary from 22° to 60°, but averaging all my trials, the result was within one-third of a degree of the elevation of the pole or latitude of the place, and much the greatest part of them taken separately were little different from that, by which it appears that these laminae are in the main parallel with the axis of the earth. In some instances, indeed, I found them perpendicular, and even reclining the other way; but these were extremely rare, and always attended with signs of convulsion, or other circumstances of singularity, which admitted a possibility of removal from their original position. These trials were made between Madison's Cave and the Patowmac. We hear of lime stone on the Missisipi and Ohio, and in all the mountainous country between the Eastern and Western waters, not on the mountains themselves, but occupying the valleys between them.

Adjacent to the vein of lime stone first mentioned, or at least to some parts of it, is a vein of slate of greater breadth than that of the lime stone, sometimes mixed with it, some times a small distance apart from it. The neighborhood of these veins of lime stone, and slate, and of lime stone and schist, between the North Mountain and Blue Ridge, coincides with the following observations of Bouguer, while in Peru: “Le marbre est tres commun sur le bord de plusieurs de ces rivieres: on y voit aussi des rochers d’ardoise & j’ai souvent eu occasion d'y observer la grande affinité qu’il y a entre ces deux sortes de pierre. J'avois deja fait cette remarque dans la Cordeliere. Les rochers de marbre et d' ardoise s’y touchent souvent, et j’en ai vu qui etoit ardoise par une extremité et marbre parfait par I'autre. Toutes les fois qui’il survient un nouveau suc pierreux analogue à l’ardoise et qui en unit les feuilles, il rend tout le rocher plus compacte et plus dur; le rocher cesse d’etre de l’ardoise pour devenir du marbre. Une pierre également distribuée par feuilles qu’on nomme schite, est aussi sujette à cette transformation. Quelquefois ce ne sont pas simplement ses feuilles qui se