PSEUDO-CONGLOMERATES IN THE ARCHEAN. 235 



that there is no reason for believing, so far as can be discovered, that any of 

 them have ever been clastic. Upon this point one paragraph is so decisive 

 that I quote it in full : * 



" Nowhere, however, in the region to which I am referring has any trace of 

 superficial eruption yet been detected. There are no true volcanic ejections, nor any 

 evidence that the rocks, though certainly of eruptive origin, were ever connected with 

 the ordinary explosive operations of volcanic vents. Not only so, but after the most 

 careful search from Sutherland to Galway not a vestige have we yet found of any 

 unquestionable sedimentary material. There are no conglomerates, no sandstones, no 

 shales ; nor even any materials that might be supposed to represent these in a meta- 

 morphosed condition. Of the actual surface of the earth these Archean rocks afford 

 no recognizable trace. They obviously did not form the superficial layer themselves. 

 They must have lain deep under a cover of other material, under which they acquired 

 their crystalline structure, and by the subsequent removal of which they have been 

 exposed to the light." 



So far as I know, the only authorities who at the present time maintain 

 that they have shown that any rocks apparently belonging to this funda- 

 mental complex f are water-deposited elastics are Dr. Alexander Wine-hell 

 and a few of the geologists of the Canadian Survey. Dr. Winchell argues 

 that certain granitic rocks iu northeastern Minnesota are conglomeratic, 

 and that the granite and gneiss of that region represent metamorphosed sedi- 

 ments. J The question immediately arises whether these rocks, if really 

 clastic, do not belong to a period subsequent to the fundamental complex. 



I will not venture to speak on this point as to the Canadian localities, and 

 Dr. Winchell answers it in the negative for the region described by him. It 

 would, however, seem to be necessary in case an unquestionable water- 

 deposited detrital rock is found, apparently as a part of the fundamental 

 complex, to show by the most positive evidence that it can not belong to a 

 later series. 



The presence of bowlder-like forms in various parts of the fundamental 

 rocks of the Lake Superior country have been somewhat widely observed by 

 Irving, Merriam, Bay ley, and myself. I have also seen like phenomena in 

 the granites of the Wasatch mountains and in those of the main Colorado 

 range. It has always appeared to me probable that these fragment-like 

 masses in the fundamental gneiss and granite in some cases represent frag- 

 ments which have been caught in eruptives in their passage to their present 

 position, and at other times represent segregations. Bearing in favor of 

 some such explanation is the extremely irregular shape which these inclu- 



* Recent Researches into the Origin and Age of the Highlands of Scotland and the West of Ire- 

 land, Archibald Geikie: Nature, Vol. 40, 1889, p. 300. 



f By this term I simply mean the most ancient known class of rocks, without implying anything 

 as to origin or expressing any opinion as to whether any portion of it represents the original crust 

 of the earth, or a part of that crust which for the first time has reached the surface. 



{Conglomerates Enclosed in G-neissic Terranes, Alexander Winchell: Am. Geol., Vol. 111,1889, 

 pp. 153-165; supplement to same, ibid., pp. 256-261. 



XXXI— Bdll. Gkol. Soc. Am., Voi 1, 1889. 



