of Lake Superior, 267 



granite is continued over the height of land, through Lakes Ke- 

 seganaga, Cypress, Couteau, and Boisblance, but in the northern 

 parts of this route*, as Lakes Namaycan, La Croix, La Pluie, and 

 of the Woods, the same greenstone frequently passes into gneis, 

 mica slate, traversed in a thousand fantastic forms, and in great 

 quantities by graphic granite ; the former rocks running E.N.E.f, 

 and dipping in a majority of instances, northerly, as Dr. Richardson 

 has observed in the lakes N.VV. of Hudson's Bay, and as occurs 

 in Lake Huron, and on the north shore of the St. Lawrence below 

 Quebec. 



The porphyry, amygdaloid, and sandstone, I consider contem- 

 poraneous ; of course, newer than the granites, §-c., above spoken 

 of; although not much, according to the transitions and alterna- 

 tions occurring about Gargantua, I am not at present prepared to 

 state the age and connexions of the greenstone trap. The sandstone 

 is, most probably, the old red, as I am led to conclude from the 

 materials composing it, its direct superposition on inclined rocks 

 in this and other of the great Lakes of the St. Lawrence, and from, 

 its supporting a blue, white, or gray chertzy limestone full of 

 productae, turbinoliae, caryophyllise, trilobites, conularise, encri- 

 nites, and orthoceratites, 8fc. 



This subject is more fully discussed in the eighth volume of the 

 American Journal of Science. 



New York, May 1, 1824. 



* Four hundred and thirty miles to the north end of the Lake of the 

 Woods. 



t In these counties there is 13". and 14°. of east magnetic variation, 

 diminishing southwards. 



T2 



