THE ARCHEOZOIC ERA 



43 



the Kewatin of the Lake Superior region, though all available evi- 

 dence strongly points to such a correlation. If this be true, it is 

 evident that the whole of the Proterozoic is absent from eastern 

 Canada and the Adirondacks where Upper Cambrian strata rest 

 upon Grenville and Laurentian. The Grenville is essentially 

 a sedimentary series, many thousands of feet thick, consisting 

 largely of gneisses, 

 quartzites, and crys- 

 talline limestones, 

 representing what 

 were once shales, 

 sandstones, and lime- 

 stones. These are 

 often distinctly 

 banded because of 

 original alternations 

 in deposition of the 

 sediments, and some- 

 times igneous rocks 

 of Grenville age ap- 

 pear to be mingled 

 with the strata. The 

 Kewatin, on the other 

 hand, is essentially a 

 volcanic series of 

 lavas and tuffs with 

 sediments in minor 

 quantity. 



It must be re- 

 membered that the 

 Archeozoic represents a vast length of time. In fact the Arche- 

 ozoic era may have been longer than all subsequent time, par- 

 ticularly if the Plane tesimal hypothesis be accepted, because, 

 according to that view, volcanic extrusions with gradually increas- 

 ing accumulation of sediments might well enough have taken 

 place long before the earth had attained anything like its present 

 size. Realizing the very great thickness of rocks and time which 

 the Archean represents, it scarcely seems probable that its base, 

 or even the base of that portion which carries sediments, is any- 

 where exposed to view. Bearing these things in mind we also see 



Fig. 21 

 Archean (Grenville) sedimentary gneiss in the cen- 

 tral Adirondacks. Note the distinct stratifica- 

 tion. (W. J. Miller, photo.) 



