MUSEUM OF COlMrARATIVE ZOOl.OOY. 109 



the majority of the observers posterior to the consolidation of the entire 

 series of rocks. They were believed to have been filled by injection by 

 Houghton, Rnggles, Jackson, Agassiz, and Marcou ; by injection and 

 sublimation, by Hodge ; b}' sublimation, by Houghton and Jackson ; and 

 in the wet way, by Foster and Whitney, Rotterniund, Miiller, Bauer- 

 man, Dawson, Pumpelly, Marvine, Hunt, and others. Hoiighton re- 

 garded the district as identical with Cornwall. The copper was 

 supposed to have been thrown from volcanoes by Schoolcraft, while 

 H. D. Rogers and Dana teach that it was deposited during the cooling 

 of the trap. Ruggles, Agassiz, and Marcou regard it as injected in 

 dikes from the molten interior, while Bauerman and Pumpelly teach 

 that it was originally deposited in the sandstone from the sea-water 

 through the reducing agency of oi'ganic matter. This view seems to be 

 shared by Hunt, who likewise, in common with Shepard, thought that 

 copper was derived from the debris of ores in the older rocks, and depos- 

 ited in the sandstones. Prof. Shepard thought that it was concentrated 

 from the sandstones, and brought to the surface by the action of the 

 traps. Whether Dr. Hunt teaches that the copper was derived directly 

 from the sandstones and deposited in the veins, or was brought up by 

 the extravasated traps, which, according to his theories, must have 

 originally formed the lower portion of the Keweenawan series, and was 

 thence concentrated in the veins, we cannot tell, for, as is frequently 

 the case in his writings, his English admits of more than one construc- 

 tion. Miiller, Bauerman, and Marvine think that the copper may have 

 been an original constituent in the traps in a finely divided condition. 

 Prof Dana teaches that it was derived from ores in the older rocks 

 by the action of the traps, and holds, with Houghton, Jackson, and 

 Shepard, that it was brought up by the trap. Foster and Whitney, 

 Dawson, ]\Iuller, Bauerman, Pumpelly, Marvine, and others, would refer 

 the concentration to electro-chemical action. Benjamin Silliman, Jr., 

 and Jackson said that the copper and silver, when foimd joined, had 

 been fused together ; while Hodge explained the phenomenon by sup- 

 posing that the copper was injected first, and by its contraction left 

 vacant spaces into which the silver was injected later. Such, in brief, 

 are some of the various theories advanced. 



The Traps. 



In order to ascertain the origin of these rocks, we have to examine, 

 first, their relation to one another, and, second, to the iuterlaminated 

 sandstone and conglomerate. 



