GEOLOGICAL EXPLORATIONS AND LITEilATUEE— 1874. 61 



Again, following the reports of the Michigan survey, there is a dearth 

 of articles of a general nature on the Marquette rocks. This period of 

 little activity was brought to an end by the publications of the Wisconsin 

 survey in 1879. A nuniljer of volumes, in which reference is made to the 

 geology of the Marquette district, were pulilished in this interval, but the 

 statements in them are largely based on the work of others than their authors. 

 A number of short articles also appeared during this time, Init they are 

 devoted mainlv to the elucidation of special points in the discussion. 



1ST4, 



Dana, J. D. 3Iaiuial of geology. 2d ed., New York, 1874. 



In the second edition of his Manual, Professor Dana makes the same 

 statements regarding the origin of the Marquette ores and of the Archean 

 rocks in general as were made in 1865, when he accepted Foster and 

 Whitney's views. With regard to the geological position of the beds, we 

 find that the author has discovered evidence enough for separating the 

 Azoic (now Archean) beds into two series, the Laurentian and the Huronian, 

 but he is not satisfied that the Marquette ores are not members of the first 

 series. On one page (p. 151) he places them with the Laurentian, and 

 on another page (p. 159) with the Huronian, mainly in deference to the 

 opinions of the Lake Superior geologists, who emphasized the lithological 

 differences between the acid schists of the Laurentian and the basic ones 

 of the Huronian. " The evidence as to age is far from conclusive," writes 

 the author. " The extent of the beds of iron ore aftbrds some reason for 

 believing, as shown by Whitney, that they are true Laurentian" (p. 159). 



Exactly the same statements concerning the ilarquette region are 

 given in the third edition of the Manual, published in 1880. 



Newberry, J. S. The iron resources of the United States. The Interna- 

 tional Review, Vol. I. 1874, pages 754-780. 



This author gives a general review^ of the iron resources of the United 

 States, and refers to the Marquette ores as magnetites, hematites, and 

 hydrated sesquioxides, inclosed in Huronian terranes. The "ore beds 

 were once horizontal strata, deposited in conformity with many other 



