518 THE AZOIC SYSTEM AND ITS SUBDIVISIONS. 



in the Sierras alike in the Hurouian schists and in the eruptive granites, which 

 probably penetrate the Huronian series." 



Dr. Hunt stated that the crystalline schists of the Sierra Nevada 

 examined by him have " all the characters of the Huronian series 

 as seen on the great lakes." (Proc. Bost. Soc. Nat. Hist, 1878, XIX., 

 p. 276.) 



In 1880 Dr. Hunt further stated that the gravel at the Blue Tent 

 placer mine, in Nevada County, California, is " made up in great part 

 of the debris of the crystalline Huronian schists of the region, including 

 much greenstone or diorite rock." (Trans. Am. Inst. Min. Eng., 1880, 

 YIIL, p. 452.) 



The present writers, having had occasion to make a prolonged and 

 most careful examination of the rocks of the Sierra Nevada, and of the 

 Coast Ranges of California, as well as of those of the south shore of 

 Lake Superior, take occasion to remark, that no such resemblances as 

 those pointed out by Dr. Hunt have any real existence. The rocks of 

 the California Coast Ranges, even where most metamorphosed, differ, 

 both microscopically and macroscopically, from those of the Sierra 

 Nevada, and specimens from the two regions in question would never 

 be mistaken for each other by any one having even a moderately well 

 trained eye. In the same way, the slaty crystalline rocks of the Sierra 

 Nevada differ nearly as much from those of the Azoic regions of Lakes 

 Huron and Superior as do the basaltic lava-flows of the latter region 

 from those of Mount ^tna. Macroscopically, the rocks of the two 

 series could never be confounded with each other, and microscopically 

 the diflFerences are equally striking. Hence it appears that, while the 

 palseontological evidence is entirely averse to the dicta of Dr. Hunt in 

 reference to the Huronian age of the Coast Range and Sierra Nevada 

 rocks, even the lithological characters are quite as little in harmony 

 with his views. Recalling what Professor Dana has remarked in refer- 

 ence to the Lower Silurian age of Dr. Hunt's "Vermont Huronian, it 

 may here be added, that the latter has, by what he has published in 

 regard to California, made out the Huronian to be also Mesozoic and 

 Tertiary, so that this formation may be said now to represent, according 

 to Dr. Hunt's views, the whole geological column from top to bottom. 



