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Updated: June 5, 2025
In the course of the geological survey carried on under the direction of Sir W.E. Logan, it has been shown that, northward of the river St. Lawrence, there is a vast series of crystalline rocks of gneiss, mica-schist, quartzite, and limestone, more than 30,000 feet in thickness, which have been called Laurentian, and which are already known to occupy an area of about 200,000 square miles.
The summit of Pundim itself is all of white rock, rounded in shape, and forming a cap to the gneiss, which weathers into precipices.
It is probable that, had they been subjected to more intense Plutonic action, they would have been transformed into hornblende- schist, foliated chlorite-schist, scaly talcose-schist, mica-schist, or other more perfectly crystalline rocks, such as are usually associated with gneiss.
It much resembles the fossil or meteoric paper of Germany, which is also formed of the lowest tribes of fresh-water plants, though considered by Ehrenberg as of animal origin. A vein of granite in the bottom of the valley had completely altered the character of the gneiss, which contained veins of jasper and masses of amorphous garnet.
The neighbouring rocks of Donkia were gneiss with granite veins, also striking north-west and dipping north-east 10 degrees, as if they overlay the limestone, but here as in all similar situations there was great confusion of the strata, and variation in direction and strike. The coolies of Dr.
The same structure may be seen in miniature on the transported blocks which abound in the Sikkim rivers; where veins of finely grained granite are forced in all directions through the gneiss, and form parallel seams or beds between the laminae of that rock, united by transverse seams, and crumpling up the gneiss itself, like the crushed leaves of a book.
In a little while we struck on the Nile, where it was running like a fine Highland stream between the gneiss and mica-schist hills of Kuku, and followed it down to near where the Asua river joined it. For a while we sat here watching the water, which was greatly discoloured, and floating down rushes.
It must be remembered that the main features of the country at Newera Ellia and the vicinity are broad flats or swampy plains, surrounded by hills and mountains: the former covered with rank grass and intersected by small streams, the latter covered with dense forest. The soil abounds with rocks of gneiss and quartz, some of the latter rose-color, some pure white.
It being assumed that columnar trap has consolidated from a fluid state, the prisms are said to be always at right angles to the COOLING SURFACES. If these surfaces, therefore, instead of being either perpendicular or horizontal, are curved, the columns ought to be inclined at every angle to the horizon; and there is a beautiful exemplification of this phenomenon in one of the valleys of the Vivarais, a mountainous district in the South of France, where, in the midst of a region of gneiss, a geologist encounters unexpectedly several volcanic cones of loose sand and scoriae.
Cambrian Rocks of the United States and Canada. Potsdam Sandstone. Huronian Series. Laurentian Group, upper and lower. Eozoon Canadense, oldest known Fossil. Fundamental Gneiss of Scotland.
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