VI.] DISTRIBUTION OF VOLCANOES. 69 



If we look at the North American continent, we find along its 

 northeastern portion evidences of great subsidence, and an accumu- 

 lation of not less than 40,000 feet of sediment along the line of the 

 Appalachians from the Gulf of St. Lawrence southwards, during the 

 palaeozoic period. This region is precisely that characterized by 

 considerable eruptions of plutonic rocks during this period and for 

 some time after its close. To the westward of the Appalachians, 

 the deposits of palaeozoic 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 from the northeast region just mentioned throughout this 

 vast palaeozoic basin, with the exception of the shores of Lake Supe- 

 rior, where we, find the early portion of the palaeozoic 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 plains of 

 northern Kussia and Scandinavia, as in the Mississippi valley, the 

 palaeozoic 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 palaeozoic strata, contorted and accompanied by igne- 

 ous 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 thick- 

 ness. It is evident that the great mountain zone which includes 

 the Pyrenees, the Alps, the Caucasus, and the Himalaya was, 

 during the later secondary and tertiary periods, a basin in which 

 vast depositions were taking place, as in the Appalachian belt dur- 

 ing the palaeozoic times. Turning to the other continental region, 

 the American Pacific slope, similar evidences of great accumulations 

 during the same periods are found throughout its Vhole 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. (Proceedings of the American Geographical Society, 

 April, 1869.) 



