f 



ADDENDA. 283 



Page 143. The limestones called the Second Magnesian, and 

 stated to be of Lower Silurian age in 2.04.17, have been lately 

 shown to be Cambrian. (G. C. Broadhead, "The Correct Succes- 

 sion of the Ozark Series," Amer. Geol, April, 1893, p. 260. F. L. 

 Nason, " The Magnesian Series of the Ozark Uplift," Ibid., Feb- 

 ruary, 1893, p. 91. A. Winslow, "Notes on the Cambrian in 

 Missouri," etc., Amer. Jour. ScL, March, 1893, p. 221.) 



Page 172. C. R. Boyd has published in the Engineering and 

 Mining Journal, June 17 and 24, 1893, a quite complete description 

 of the lead and zinc mines and works of the Wythe Company, near 

 Austinville, Va. The geological horizon is stated to be in the 

 Knox group of Safford, which is, as stated in the text, near the 

 Calciferous of New York. While giving a thorough historical 

 sketch and description of the works, little additional to the brief 

 outline on p. 172 is given on the geology. 



Page 247. Mr. Waldemar Lindgrenhas published (June, 1893) 

 in the Bulletin of the Geological Society of America, Vol. IV., 

 pp. 257-298, a most valuable paper on "Two Neocene Rivers of 

 California." He traces out the location and geological history of 

 the deep gravels along the drainage line of the American and Yuba 

 rivers, and adds much to our knowledge of their former location 

 and gradients. He concludes that the old divide in general coin- 

 cided with the present one, but that the slope of the Sierra has 

 been considerably increase 1 since the time when the Neocene (i.e., 

 Miocene and Pliocene), ante-volcanic rivers flowed over its surface. 

 " It finally appears probable . . . that the surface of the Sierra 

 Nevada has been deformed during this uplift, and that the most 

 noticeable deformation has been caused by a subsidence of the 

 portion adjoining the great valley, relatively to the middle part of 

 the range " (p. 298). 



General Addenda. I. Through the courtesy of Dr. R. W. 

 Raymond, secretary of the American Institute of Mining Engineers, 

 the author has been permitted to read, in advance of its pub- 

 lication, the great essay on the origin of ore deposits, that Prof. 

 Franz Posepny of Vienna has sent to the Institute for the July 

 meeting, 1893. The paper is a theoretical discussion of the origin 

 of ores, with illustrations selected from all parts of the world, but 

 especially from Europe and America. It forms one of the most 

 important contributions to the literature that has yet been made. 

 Posepny distinguishes at the outset between rocks and mineral 

 deposits ; i.e., between original materials, such as wall rock, and 



