i 



h ' 



MICHIGAN AND WISCONSIN, 



493 



Mr. T. B. Brooks ; consequently numerous statements are put forth by 

 him as original, when in fact they had been previously published by 

 others. Had Dr. Rominger been more conversant with the literature 

 of the district, many errors into which he has fallen would have been 

 spared him, since he is essentially a palicontologist. However, he ap- 

 pears to have worked conscientiouslj^ and to have endeavored tO' ascer- 

 tain the truth so far as he could. 



Regarding the so-called Laurentian granites. Dr. Rominger states : — 



" According to my own observations the granites of Marci^uette are eruptive 

 masses which came to the surface after the Huroiiian beds were already formed, 

 and by their eruption caused, not only the great dislocations of the Hnroidan 

 formation, but the half molten plastic granite masses induced by their contact 

 with the lluronian rock-beds, also their alteration into a more or less perfect 

 crj^staljine condition, and commingled with thexn so as to make it an embar- 

 rassing tnsk to find a line of demarcation between the intrusive and the in- 

 truded rock- masses." (I. c, p. 6.) 



^ 



He also pointa to the fact that lamination is no proof of stratification, 

 stating that he had **in several instances seen narrow intrusive granitic 

 dyke-masses similarly laminated 'by the parallel arrangement of the 

 mica scales in them." (/. c, p. 16.) 



Dr. Rominger further proceeds : 



" The granites, considered in their present surface position, are, in relation 

 to the stratified sedimentary rocks of the Huronian serieS, actually the younger 

 rock, so far as the intrusion of very large masses of granite between the strati- 

 fied sediments can be demonstrated by clearly observable facts, and as tjie 

 other larger bodies of granite inclosing them [the so-called Huronian schists] 

 from two sides are in direct continuity with the vein granites, and lithologi- 

 cally identical with them." {l. c, p. 22.) 



I 



Whilo Dr. Rominger regarded part of the basic rocks as truly erup- 

 tive in the form of dikes and lava flows, he recognized also the intrusive 

 nature of much of the remainder ; but being unable, from lack of litho- 

 logieal training, to distinguish between the older ei^iptives and their 

 associated schistose rocks, he — like Mr. Brooks — confounded them to- 

 gether, and adopted for explanation the following theory, difficult of 

 comprehension, and certainly not at all consonant with the facts ob- 

 served in the district, the difficulty lying with the observers, and not 

 with the rocks : — 



" From such a standpoint, the various crystalline hornblende rocks found in 

 association with the granites could be considered as remelted, completely 

 metamorphosed, Huronian sediments, on account of their nearest proximity to 



i ■ 



* 



w n 



