of Lake Superior. 243 



essential aid in determining their relative ages. About seven 

 miles from the crags, or somewhat more to the west, the green- 

 stone trap loses its irregularity of outline, and assumes the form 

 of veins or dykes, which are most numerous during the next ten 

 miles ; but, as they prevail in this and other rocks as far as Thunder 

 Mountain, 1 prefer giving them a separate notice at the close of 

 my remarks on the granite now under consideration. This granite 

 is by no means the exclusive occupant of the coast to the Otter's 

 Head. Having been very variable in its quantity of hornblende 

 in the interval, at seventeen miles from the Otter's Head it is re- 

 placed by greenstone for three leagues of very broken country. 

 This greenstone is massive, in low ruinous ledges, or mural cliffs 

 with perpendicular fissures. It is quite black, granular, or small 

 crystalline; or it is the massive pale greenstone of Michipicoton, 

 the colour changing irregularly : occasionally, indeed, an east 

 direction is visible (or EbN.), the dip being either vertical or 

 northerly. About nine miles and a half from the Otter's Head, 

 the greenstone has a distinctly east direction and northern incli- 

 nation. It here changes colour and composition in a striking 

 manner, transversely to the direction, and insensibly. The horn- 

 blende disappears, and a red schistose jaspery matter is substi- 

 tuted, which becomes black, brown, and gray quartzy slate, with 

 just sufficient mica to create a gloss. In the space now under 

 notice the trap veins are seen to cross from the granite to green- 

 stone. 



In the eight miles next to the Otter's Head the whole distance 

 is occupied by granife alternating with greenstone, the former 

 being now and then almost altogether red feldspar and white 

 quartz, and at other times being full of hornblende. These alter- 

 nations aro particularly striking near the east side of the Otter's 

 Head. 



About a mile from it a rugged eminence of slaty greenstone from 

 400 to 500 yards broad, and from 150 to 200 feet high is stra- 

 tified E. or EbN. perpendicularly, each layer being about eighteen 

 inches thick. It is of the Michipicoton species, and changes its 

 colours as usual. The jaspery substance is here present, which 



