146 ARCHAEAN TIME. 



tween great continental basins that were, in a marked degree, inde- 

 pendent in the progress of rock-making and of life. The positions of 

 the mountain chains, and of other prominent features of the land, were 

 thus indicated long before they had existence. It will be convenient, 

 therefore, to describe the rocks, and sometimes the life, of each such 

 region separately; and these regions are therefore here enumerated. 



1. The Eastern Border basin or region, east and northeast of the 

 Green Mountain range, and including New England, Eastern Canada, 

 New Brunswick, western Nova Scotia, the Gulf of St. Lawrence and 

 Newfoundland. 



2. The Appalachian region, along the course of the Appalachians, 

 through the Green Mountains, to the vicinity of Quebec. 



3. The Interior Continental basin, between the Appalachians (with 

 the Green Mountains, properly the northern part of them) and the 

 Rocky Mountain chain. 



4. The Western Border basin, west of the Rocky Mountain 

 summit. 



A great Arctic Border region and a Rocky Mountain region may 

 hereafter be recognized ; but the facts thus far collected do not at 

 present make it necessary to refer separately to them. 



I. ARCH^AN TIME. 



Archsean time includes strictly, as its commencement, an Azoic age, 

 or the era in which the physical conditions were incompatible with 

 the existence of life. But this era, so far as now known, is with- 

 out recognizable records ; for no rocks have yet been shown to be 

 earlier in date than those which are now supposed to have been 

 formed since the first life began to exist. About this early era there 

 is, therefore, little known. By following the lead of ascertained law 

 in physics and chemistry, and the suggestions of astronomy, and also 

 analogies from later geological history, some probable conclusions may 

 be reached. But this is not the place for their discussion, except so 

 far as to state the principal steps of progress. There must have 

 been, — 



I. A first era, after that of the original nebula, if such there was, 

 — in which the earth was a globe of molten rock, like the sun in 

 brightness and nature, enveloped in an atmosphere containing the 

 dissociated elements of the future waters and whatever else the heat 

 at the surface could throw into a state of vapor. 



II. A second era, in which cooling went forward until, in the first 

 place, the earth became solid at centre, pressure causing the solidifica- 



