20 LAURENTIAN SYSTEM. 



and probably more than eight miles, or quite as great as it is in Bohemia or any 

 other European country. 



35. While these are the oldest rocks known, they were, in their unmeta- 

 morphosed condition, ordinary sediment in water derived from materials that pre. 

 ceded them. They were formed by the disintegration, denudation, and redeposi- 

 tion of older rocks, which in their turn preceded others, in how many cycles of 

 change we have no means of knowing. Their upheaval above the surface of the 

 sea was the beginning of the North American continent. The trend of the range 

 in this upheaval is as nearly east and west as the later elevations of the Appalachian 

 and Kocky Mountain chains are north and south. These rocks were until recently 

 supposed to have preceded the existence of both vegetable and animal organisms, 

 and were, therefore, called azoic, but in addition to the fossil Eozoon canadense there 

 are other evidences of organic life, as follows : 



1. The iron ore evidences organic life, because all the accumulations of iron 

 now in progress are formed by the agency of organic matter. The peroxide of 

 iron existing in the rocks is not soluble in water alone, but the addition of decom- 

 posing organic matter deoxidizes it, and carbonate of iron is formed, which is 

 soluble and may be precipitated. Peroxide of iron being insoluble, the infiltrating 

 waters which take up soda, lime, and magnesia from sediments, can not remove this 

 metal unless they contain organic matter. The evidence of the reducing and dis- 

 solving action of organic matter is, in the great thickness of sediments, almost des- 

 titute of iron and in the extensive beds of iron ore. 



2. The masses of limestone tend to prove the existence of organic matter, be- 

 cause limestone in process of formation is almost wholly composed of shells, corals, 

 tests of foraminifera, and other animal secretions, and nearly all the unmetamorphosed 

 limestones of past ages are largely composed of organic relics. 



3. Graphite occurs in beds, imbedded masses, and in scales ; in granite, gneiss, 

 mica schist, and crystalline limestones ; it results from the alteration by heat of coal 

 in the Coal Measures, and is a common product of furnaces. Its presence is, 

 therefore, an evidence of organic matter, because we know of no other source for its 

 derivation, and are able to trace its origin to vegetable matter in rocks of a less 

 remote date. It is inferred the carbon was collected by marine vegetation at that 

 early period. 



4. In the lowest non-metamorphosed rocks, and in the shales and limestones of 

 the Taconic System, several classes of the animal subkingdom are represented, 

 which indicates, if we judge by analogy with subsequent changes and progress of 

 life, that the seas in much earlier times must have teemed with life. This is the only 

 view consistent with the modern theory of evolution and the present state of 

 knowledge concerning the development of animals and vegetables. 



5. The Eozoon canadense, a fossil rhizopod, is found in the Grenville band of 

 limestone near the middle of the series. The limestone is thus described: "The 

 general character of the rock connected with the fossil produces the impression that it 

 is a great foramiuiferal reef, in which the pyroxene masses represent a more ancient 

 portion, which, having died and become much broken up and worn into cavities and 

 deep recesses, afforded a seat for a new growth of foraminifera, represented by the 

 calcareo-serpentinous part. This in its turn became broken up, leaving, however, 

 in some places, uninjured portions of the organic structure. The main difference 



