on American Geology, 97 



west, as this shore-derived material diminishes in volume, the 

 amount of calcareous matter rapidly augments. Mr. Hall concludes 

 therefore that the coal-measure sediments were driven westward 

 into an ocean, where there already existed a marine fauna. At 

 length, the marine limestones predominating, the coal measures 

 come to be of little importance, and we have a great limestone 

 formation of marine origin,which in the Rocky Mountains and New 

 Mexico occupies the horizon of the coal, and itself unaltered, rests 

 on crystalline strata like those of the Appalachian range. In 

 truth, Mr. Hall observes, the carboniferous limestone is one of the 

 most extensive marine formations of the continent, and is charac- 

 terized over a much greater area by its marine fauna than by its 

 terrestrial vegetation. 



" The accumulations of the coal period were the last that gave 

 form and contour to the eastern side of our continent, from the 

 Gulf of St. Lawrence to the Gulf of Mexico ; and as we have shown 

 that the great sedimentary deposits of successive periods have 

 followed essentially the same course, parallel to the mountain 

 ranges, we naturally inquire : What influence this accumulation 

 has had upon the topography of our country, and whether the 

 present line of mountain elevation from north-east to south-west 

 is in any way connected with the original accumulation of 

 sediments?" HalVs Introduction^ p. QQ. 



The total thickness of the palaeozoic strata along the Appala- 

 chian chain is about 40,000 feet, while the same formations in the 

 Mississippi valley, including the carboniferous limestone, which is 

 wanting in the east, have according to Mr. Hall, a thickness of 

 scarcely 4000 feet.* In many places in this valley we find the 

 Silurian formations exposed, exhibiting hills of 1000 feet, made up 

 of horizontal strata, with the Potsdam sandstone for their 

 base, and capped by the Niagara limestone, while the same strata 

 in the Appalachians would give from ten to sixteen times that 



* In Michigan, according to the late report of Prof. Winchell, the total 

 observed thickness of the strata from the top of the Sault St. Mary 

 sandstones to the top of the carboniferous series is little over 1790 feet, 

 divided as follows : — Trenton and Hudson River groups, 50 feet, Upper 

 Silurian 185, Devonian 782, Carboniferous tOO ; of this last the true coal 

 measures constitute 123 feet, including from 3 to 10 feet of workable 

 bituminous and cannel coals, while near the base of the carboniferous 

 series are found 169 feet of gypsiferous marls, which yield strong brine 

 springs. 



Can. Nat, 2 Vol. VI. No. 2. 



