THE ARCHEOZOIC ERA 443 



It would indeed be difficult to obtain an exaggerated idea of 

 the complexity of the rock which has caused this system to be 

 called the "Archean Complex/' the "Basement Complex/' the 

 " Fundamental Complex/' etc. The rocks of no later era are so 

 generally and so notably deformed, or so generally and so highly 

 metamorphic. Because of these complications, the interpretation 

 of these rocks is difficult, and such views of their classification and 

 correlation as are now entertained are to be held subject to emen- 

 dation as knowledge advances. 



DISTRIBUTION AND LOCAL DEVELOPMENT 

 General distribution. The Archean is the one accessible rock 

 system which, theoretically, completely envelopes the globe. No 

 later system does this, for wherever the Archean comes to the sur- 

 face, later formations are absent. 



In speaking of the distribution of a formation, its distribution 

 at the surface is generally meant, and in speaking of its surface 

 distribution, the mantle rock (glacial drift, etc.) which overlies 

 and conceals it is usually ignored unless it is so thick as to make 

 the underlying formation indeterminable. When the surface 

 distribution of the formation is given, therefore, it is not to be 

 understood that the formation is literally at the surface everywhere 

 within the area specified, but rather that it is exposed here and 

 there within that area, and that between the points of exposure 

 it is the uppermost formation beneath the mantle rock. In this 

 sense, the Archean rocks are estimated to appear at the surface 

 over about one-fifth of the area of the land; but since great areas 

 in some continents have only been reconnoitered geologically, this 

 figure is only a rough estimate. 



In North America, 1 by far the largest area of Archean rock 



1 The literature on the Archean (as well as Algonkian [Proterozoic] ) of 

 North America was summarized by Van Hise in Bull. 86, U. S. Geol. Surv., 

 in 1892. This publication gives full bibliography to its date. A later (1896) 

 and briefer summary of the same subjects by the same author was published, 

 Pt. II, 16th Ann. Kept., U. S. Geol. Surv., pp. 744-843. The pre-Cambrian 

 literature since 1892 has been summarized from time to time by the same 

 author, and by Leith, in the Jour, of Geol., as follows: Vol. I, pp. 304 and 532; 

 II, pp. 109 and 444; III, pp. 227 and 709; IV, pp. 362 and 744; VI, pp. 527, 

 739, and 840; VII, pp. 190, 406, 702, and 790; VIII, p. 512; IX, pp. 79 and 

 441; and XII, pp. 63 and 161. 



