FUNDAMENTAL PROBLEMS OF GEOLOGY. 253 



amount of material poured out on the surface in molten form or 

 introduced into the outer parts of the earth from below was very- 

 much greater than the accessions from without. Still later, these 

 declining accessions were so overwhelmed by the igneous extrusions 

 that they became indistinguishable contributions. In this stage, too, 

 it is held that the modifications wrought by the atmosphere, the 

 hydrosphere, and organic life were also quite subordinate to the 

 volcanic contributions. Disintegration is assumed to have gone 

 little farther, usually, than to partially reduce rocks of the granitoid 

 type to arkoses, and those of the basic type to wackes. Rather 

 rarely, it is believed, was much pure quartzose sand, aluminous clay, 

 or similar well-decomposed residuary materials accumulated ; rarely, 

 also, much carbonaceous shale. Arkoses and wackes, when meta- 

 morphosed later, took on such a similitude to igneous rocks as to be 

 more or less unidentifiable. 



The formations of this period of volcanic dominance, with very 

 subordinate clastic accompaniment, are regarded as constituting the 

 Archean complex, though perhaps only the later portions of the 

 great volcanic series are represented by the known Archean. 



I have studied at considerable length the problem of deformation of 

 the earth under the several hypotheses of its origin and the conditions 

 sequent thereon. The most difficult feature is to bring into working 

 harmony the agencies that produce lateral thrust of the outer crust as 

 demonstrated in the extensive folding and reverse faulting, on the 

 one hand, and the vertical movements exemplified in plateaus and 

 normal faulting on the other. Current views are attended by grave 

 difficulties when an attempt is made to reduce them to quantitative 

 terms. I have developed what appears at present a very promising 

 line of solution, but I prefer to work upon it somewhat further before 

 reporting upon it. 



I desire to direct attention to the fact, frequently indicated by allu- 

 sions in the preceding statement, that further deplo3'ment, and par- 

 ticularly further testing of the hypotheses and sub-hypotheses, all 

 along the line, are definitely contemplated. While they have been 

 constructed with some hope that they may be in the line of the ulte- 

 rior truth, it is felt that their only assured value lies in the aid they 

 may render in the development of tributary investigations, and in 

 assembling and interpreting the varied data from the multitude of 

 sources from which so complex a problem must necessarily make 

 drafts. The accompanying communication of Dr. Moultou indicates 

 in particular that a severe testing of our own hj-potheses, as well 

 as those of others, is a part of our working scheme. 



