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nevertheless somewhat depressing to consider on how many important 

 questions connected with this, the most common and ordinary of all 

 the plutonic rocks, there are still grave differences of opinion among 

 those justly considered as authorities. Thus all do not agree even as 

 to the order of the crystallization of the constituents of the rock, some 

 holding that there are two generations and others that there is but one, 

 while again a marked difference of opinion exists concerning the effects 

 produced by granite upon the rocks through which it is intruded. 



As the result of a whole series of careful studies on various contact 

 zones, chiefly in Germany, Austria, and Scandinavia, it is commonly 

 believed in these countries that the granite magma, by its heat, pres- 

 sure and escaping vapors, causes a recrystallization of the country rock, 

 the process being one of diagenesis, the granite giving nothing to the 

 rock through which it breaks, except in places, perhaps, a small amount 

 of boracic acid. 



In France, however, and everywhere within the French "sphere of 

 influence" different opinions prevail, and it would actually appear 

 from the studies made in these parts of Europe that the laws of nature 

 changed upon crossing the political boundaries. Contact zones have 

 been described by Barrois, Michel-Levy, Delage, and other French 

 petrographers, in which the country rock adjacent to the granite has 

 become completely "granitized" by the transfusion of granitic material 

 into it, and in a well-known paper by Michel-Levy, which appeared in 

 1887,' he stated it as his belief that by this piocess gneisses, leptynites, 

 dolomitic schists and amphibolites, indistinguishable from those of the 

 Archaean, are produced, and that in fact the so-called primitive rocks 

 have really originated in this way, by the intrusion of igneous rocks 

 into clastic sediments, which sediments have undergone a profound 

 metamorphosis with the addition of an immense mass of material, the 

 process being essentially one of a metasomatosis. 



In the first section of the Bulletin, whose title is given above, 

 Michel-Levy describes an additional contact zone of this kind occurring 

 about the granite of Flamanville, which granite cuts shales, sandstones, 

 and quartzites, chiefly of Silurian and Devonian Age. On approaching 

 the granite the shales present successively the usual zones of the spot- 

 ted clay slate, micaceous clay slate, and hornstone, but in the vicinity 

 of the actual contact they are broken up, eaten into, and partially dis- 



' Sur I'orijine das terrains cristallins primitifs. Bull. Soc. Geol. de France, ^'T 

 s.Siy, 103. 



