396 THE CANADIAN NATURALIST. [Dec. 



churacterized by considerable eruptions of plutonic rocks during 

 this period and for some time after its close. To the westward of 

 tlie Appalachians, the deposits of paleozoic sediments were much 

 thinner, and in the Mississippi valley are probably less than 

 4,000 feet in thickness. Conformably with this, there are no 

 traces of plutonic or volcanic outbursts trom the north-east region 

 just mentioned throughout this vast paleozoic basin, with the 

 exception of the region of Lake Superior, where we find the early 

 portion of the paleozoic age marked by a great accumulation of 

 sediments, comparable to that occurring at the same time in the 

 region of New England, and followed or accompanied by similar 

 plutonic phenomena. Across the p'ains of northern Russia and 

 Scandinavia, as in the Mississippi valley, the paleozoic period was 

 represented by not more than 2,000 feet of sediments, which still 

 lie undisturbed, while in the British islands 50,000 feet of 

 paleozoic strata, contorted and accompanied by igneous rocks, 

 attest the connection between great accumulation and plutonic 

 phenomena. 



Coming now to modern volcanoes, we find them in their 

 greatest activity in oceanic regions, where subsidence and 

 accumulation are still going on. Of the two continental regions 

 already pointed out, that along the Mediterranean basin is 

 marked by an accumulation of mesozoic and tertiary sediments, 

 20,000 feet or more in thickness. It is evident that the great 

 mountain zone, which includes the Pyrenees, the Alps, the 

 Caucasus and the Himmalaya, was, during the later secondary 

 and tertiary periods, a basin in which vast accumulations of 

 sediments were taking place, as in the Appalachian belt during 

 the paleozoic times. Turning now to the other continental region, 

 the American Pacific slope, similar evidences of great accumulations 

 during the same periods are found throughout its whole extent, 

 showing that the great Pacific mountain belt of North and South 

 America, with its attendant volcanoes, is, in the main, the 

 geological equivalent or counterpart of the great east and west 

 belt of the eastern world. 



It is to be remarked that the volcanic vents are seldom 

 immediately along the lines of greatest accumulation, but appear 

 around and at certain distances therefrom. The question of the 

 duration of volcanic activity in a given region is one of great interest, 

 which cannot, for want of time, be considered here. It appears 

 probable that the great manifestations of volcanic force belong to 



