GENERAL CONSIDERATIONS 681 



reference to their trend-lines. This is a fundamental consideration in 

 Euedemann's paper, and in his summary regarding the principal lines 

 of pre-Cambrian folding in North. America he says : 



"The northeast of North America, including Greenland, exhibits a distinct 

 northeast direction. . . . This northeast direction swings in the interior of 

 the continent into an east-west line, and the latter turns into a north-south 

 line as it approaches the Rockj- Mountain region. The pre-Cambrian folding 

 of North America exhibits thus a grand and simple curvature (see accom- 

 panying map), which clearly proves this part of the earth to have acted as 

 one unit against the diastrophic forces active in pre-Cambrian time." 



Euedemann's conclusions regarding the trend of pre-Cambrian folds 

 and foliation should not go unchallenged ; for, as a glance at the accom- 

 panying map shows, most of the actually observed strikes of pre-Cam- 

 brian folds and foliation fall far short of warranting the representation 

 of these structures in the form of "a grand and simple curvature." 



Before proceeding to a discussion of observed strikes of pre-Cambrian 

 structures, attention should be directed to certain important general con- 

 siderations which must be constantly kept in mind in any attempt to 

 deal with pre-Cambrian diastrophism. 



GeNEKAL CONSJDEKATIONS 

 DEGREE OF FOLDING OF EARLIER PRE-CAMBRIAX ROCKS 



Most writers on the subject seem to take it for granted that the earlier 

 pre-Cambrian rocks are everywhere severely folded and highly meta- 

 morphosed. Ruedemami, for example, states (page To) "that the 

 Archean basement complex has undergone not only complete meta- 

 morphism, but also a worldwide intense folding." The present writer 

 believes that the facts for certain (or possibly many) regions are op- 

 posed to such a sweeping assertion. He published a rather elaborate 

 ]:)aper^ in 1916 in which, after critically examining the field facts and 

 the views generally held, he concluded that the whole Adirondack area 

 of earlier pre-Cambrian rocks, excepting the extreme northwestern side, 

 has never been subjected to anything like severe orogenic pressure, and 

 that the influence of the large-scale magmatic intrusives, accompanied 

 by not more than very moderate lateral pressure, more satisfactorily 

 explains the rock structures. The Adirondack Grenville (Archean) sedi- 

 mentary series generally has its stratification remarkably preserved, and 

 many large areas of the rock are either in nearly horizontal position or 

 show only moderate tilting'. Ruedemann states that these rocks have 



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

 XLV — Bull. Geol. See. Am., Vol. 34, 1922 



