As far as it has been explored, the general geological structure of Canada exhibits a granite country, with some calcareous rocks of a soft texture in horizontal strata. The lower islands in the St. Lawrence are merely inequalities of the vast granite strata which occasionally stand above the level of the waters; the whole neighboring country appears as if the Great River had at one time covered it. The banks of the St. Lawrence are in many places formed of a schistus substance in a decaying state, but still granite is every where found in strata, inclined, but never parallel to the horizon. In the Gaspe District, many beautiful quartz, and a great variety of cornelians, agates, copals, and jaspers have been found, and traces of coal have also been observed.[152] The north shore of the St. Lawrence, from thirty miles below Quebec eastward, and along the coast of Labrador, is generally of the primitive formations. Except in the marshes and swamps, rocks obtrude upon the surface in all quarters; in many places, deep fissures of from six inches to two feet wide are seen bearing witness to volcanic violence; the Indians describe some of these rents as several miles long, and forty or fifty deep; when covered with the thick underwood, they are, at times, very dangerous to the traveler. These chasms are probably owing to some great subterranean action; there is a manuscript in the Jesuits' College at Quebec which records the occurrence of an earthquake on the 5th of February, 1663, at about half past 5 P.M., felt through the whole extent of Canada: trees in the forests were torn up and dashed against each other with inconceivable violence; mountains were raised from their foundations and thrown into valleys, leaving awful chasms behind; from the openings issued dense clouds of smoke, dust, and sand; many rivers disappeared, others were diverted from their course, and the great St. Lawrence became suddenly white as far down as the mouth of the Saguenay. The first shock lasted for more than half an hour, but the greatest violence was only for fifteen minutes. At Tadoussac, a shower of volcanic ashes descended upon the rivers, agitating the waters like a tempest. This tremendous earthquake extended simultaneously over 180,000 square miles of country, and lasted for nearly six months almost without intermission.[153]