81 



DESCRIPTIONS OF STRATA, ACCORDING TO THE 

 FOREGOING SERIES.* 



Class. I. Primitive, or First Series. 

 1. Granite, is an aggregate of angular masses of quartz, 1. Carbo 



^ , , . , . „ , niferous fur 



felspar, and mica. bubdivisions. it is called crystaliine mation. 

 (granite proper) when the felspar and quartz present a crys- 

 talline, not a slaty, form. It is called (gneiss) when the 

 mica is so interposed in layers as to present a slaty form. — • 

 Varieties. It is graphic when the felspar is in a large pro- 

 portion, and the quartz is arranged in oblong masses, so as to 

 present an appearance resembling Chinese letters. It is por- 

 phyritic when spotted with cuboid blocks of felspar. This 

 variety is peculiar to the slaty division. 



Localities. — McComb's Mts.t At West Point we find as 

 extensive layers of crystalline granite, as at any place which 

 I have visited. Here it always alternates with the slaty subdi- 

 vision (gneiss.) It is the same at Chesterfield, Goshen, 

 Southampton, Russel, Spencer, &c. in Massachusetts. Also 

 in Haddam, Litchfield, Norfolk, &c. in Connecticut. These 



* Every rock consists, essentially^ of one, two or three, of the following nine 

 homogeneous minerals. These are called tlie geological alphabet ; and^every 

 student mmt procure, and familiarize himself with,.a specimen of each, before 

 he commences the study of geology— quartz, felspar, mica, talc, hornblende, 

 argillite, limestone, gypsum, chlorite. He should procure also a specimen of 

 iron pyrites, hornstone, calc spar, reddle ore, bog-ore, glance coal, bitumin- 

 ous coal, and plumbago. 



•f- It appeaVs by the map, that the primitive rocks of McComb's Mts. incline 

 obliquely in a northwesterly direction, crossing the St.Lawrence at Ogdensbur^. 

 Mr. Goodsell of Rochester collected a suit of specimens in the islands of the St. 

 Lawrence, and on the main land, for a consideiable distance into Canada. Jii 

 the month of August and September, 1828, Lieut. Day, at the request of Dr 

 Zina Pitcher, collected a series of rock specimens from "lake Huron to Montreal' 

 on both sides of, and upon, the mountain ridge, which runs along the north side 

 of the great chain of lakes. These specimens I have before nie. Also a suit 

 collected by Dr. Pitcher himself, presenting the entire geology of the whole 

 circuit of Lake Superior. I am now prepared to inform Amencan geologists 

 that the McComb Mt. range of primitive rocks extend, in a northwest direction' 

 forming the north-eastern boundary of the great lakes ; at least to the distance' 

 of one thousand miles from the St. Lawrence at Ogdensburg. I intend to give 

 a general account of the geology of those northwestern regions, in the course of 

 the year, m Sjllmian's Journal, from specimens and by the aid of Dr Pitcher 

 of the U. S. Army, unless that gentleman will himself undertake it. 



