AZOIC AGE. 185 



America. It is with great truth, then, that Agassiz says 

 that, though America is called the New World, she is 

 really the Old World, for she is really first-born among 

 continents. 



268. Thickness of the Azoic Strata. The strata of the 

 azoic rocks varies from twenty to thirty thousand feet in 

 thickness. An immensely long period was required to 

 deposit and solidify so much material, and comparative 

 quiet must have reigned during their deposit. The up- 

 heavals occurred after this was done. 



269. Upheavals and Bondings. These are very exten- 

 sive, and there is much regularity in them, for the strike 

 is the same in some cases over great extents of territory. 

 The regularity is most observable in the strata of the lat- 

 ter part of the age, for in the first part the heat was so 

 great that the rocks then formed are much contorted. 



270. Rocks of the Azoic Age. The rocks of this age 

 are granite, gneiss, schists, limestones, etc. They were 

 mostly deposited in beds, and then were crystallized 

 chiefly by the influence of the great heat which pre- 

 vailed in that age. Some of the granite is metamorphic, 

 but some of it was made originally as granite, having 

 been forced upward from below, as was often done at 

 different periods in the succeeding ages. One character- 

 istic of the azoic rocks is the prevalence of iron. Some 

 of the minerals which enter into the composition of some 

 of the rocks contain iron, and there are sometimes found 

 in the strata beds of iron ore of greater extent than in 

 any other age. 



271. Heat and Light in the Azoic Age. The heat of 

 the forming crust in the first part of this age must have 

 been very great, and the upheavings and commotions 

 must then have been tumultuous. Hugh Miller thus de- 

 scribes what may be imagined to be the state of things 

 at that time. "Let us suppose that during the earlier 

 part of this period of excessive heat the waters of the 

 ocean had stood at the boiling point even at the surface, 



