OBSERVED STRIKES OF PRE-CAMBRIAN TOLDING AND FOLIATIOX 691 



formed (indicated by circle on the map) until the Eocky Mountain fold- 

 ing of the early Tertiary. 



Of the relatively few definitely known pre-Cambrian structure lines 

 within the vast area of the western half of Canada, therefore, only part 

 of those by Camsell in the Athabasca Lake region are even approximately 

 in harmony with the trend-line announced by Ruedemann. 



EASTERN UNITED STATES 



Northern New YorJc. — The writer has for many years been making 

 detailed studies throughout the Adirondack Mountain region, and, as 

 already pointed out in this paper, he does not believe that this whole 

 region of earlier pre-Cambrian rocks was ever very notably folded. 

 Xeither does the writer believe that there is a distinct northeast struc- 

 tural trend throughout the district. The strikes, which are mostly mag- 

 matic flow structure lines and jDartly foliation of tilted blocks of meta- 

 morphosed strata, are exceedingly irregular throughout the Adirondacks. 

 The acttial facts and their significance are dealt with at some length in 

 a 23aper^° published a few years ago. 



The writer agrees with Euedemann that the area from the northwest- 

 ern border of the Adirondacks to the Thousand Islands has probably been 

 more or less notabl}^ folded with a general northeast trend, but this area 

 is really outside of the Adirondack district, which is 120 miles across and 

 in which the structural conditions are different. It is but necessary to 

 glance at the New York State Museum geologic maps made by the writer 

 and others, representing many portions of the region, in order to realize 

 that the facts do not warrant the conclusion that the pre-Cambrian rocks 

 of the Adirondacks show a distinct northeast folded structure. As al- 

 ready mentioned, Collins says that a northeast structural trend through 

 Quebec and Ontario is not nearly as persistent and clearly defined as has 

 generally been assumed. This idea of persistence of trend appears to 

 have originated many years ago, when knowledge of the pre-Cambrian 

 structure of eastern Canada and northern Xew York was largely con- 

 fined to the Saint Lawrence Yalley region, in which a northeast trend 

 does prevail. 



New England. — In both western and southeastern N"ew England belts 

 of pre-Cambrian rocks show a general north-south trend, but this struc- 

 ture has largely or wholly resulted from a high degree of infolding with 

 Paleozoic strata ; and so this structure has no significance in our present 

 discussion. Mr. Arthur Keith has, however, recentlv stated to the writer 



" W. J. Miller : Jour. Geol.. vol. 24. 1916, pp. 587-612. 



