BLENDING OF MINERALOGICAL CHARACTARS. 375 



Furthermore, the facts which I have cited in reference to the interbedding 

 of gneisses and schists show that, while each stratum retains a characteristic 

 individuality, this is something which depends, first, upon relative richness 

 in feldspar, and, second, upon the coloration and relative proportions of the 

 other two essential constituents. The very facts of the geologically rapid 

 alternation of gneiss and schists argues the persistence of the same petrogenic 

 forces and their indifference to the relative proportions of feldspathic ele- 

 ments. It is easy to believe, however, that some change in addition to that 

 of the supply of material takes place when the formation becomes schistic, 

 and that an seonic change may be conceived as inaugurating the formation of 

 the great body of the crystalline schists ; but, as I am here dealing only 

 with observed facts, I repeat, no mineralogical alternations are found in the 

 zone of lithological alternations except the changes in the proportions of 

 feldspar. 



The indifference of Nature to a greater or less proportion of feldspar is 

 indicated by the fact observed in some cases that in the local passage from 

 the schistoid to the gneissoid phase the schistoid aspect melts into the 

 gneissoid, and the resulting rock is simply the product of their interblend- 

 ing. 



The facts stated in these paragraphs have been with me the subject of 

 common observation ; but the conclusion which I base on them is decidedly 

 in conflict with prevailing opinion ; and I shall make a few citations from 

 the recorded observations of ofher geologists upon similar rocks. At a 

 certain locality on the Little Fork river, Mr. H. V. Winchell describes the 

 situation as follows : 



"Just below, around the point, is an outcrop of mica schist interbedded with thin 

 beds of gneiss. * * * It [the schist] is quite thin bedded and is the characteristic 

 rock of this whole region. In places it is hard to say which is schist and which is 

 gneiss or where one bed stops and the other commences, and, again, they are separated 

 quite distinctly.' 1 * 



Speaking of a locality on the south shore of Rainy lake, the same observer 

 says: 



"In the southwest quarter of section 25, in the same township [71-23], this diabase 

 has all graduated into a rock that is very plainly gneiss, and, going a little farther 

 south across the strike, it is still farther changed into a thin-bedded gneiss and finally 

 into mica schist with the ordinary strike and dip." f 



Of the occurrence at another point on Rainy lake the same authority 

 reports : 



" At this place is a bed of gneiss that cuts across the schist for some distance, then 

 comes into conformity with it, and all at once splits up into thin beds an inch or two 

 thick and becomes lost in the schist." J 



* Sixteenth Ann. Rep. Minn. Surv., pp. 405-6. 

 t Ibid., p. 415. 

 % Ibid., p. 419. 



