Geology and Mineralogy. 173 



3. A neic locality for Silurian Limestone in Northern Michi- 

 gan ; by A. E. Seaman. (Communicated). — In view of the fact 

 that much has been written about Limestone Mountain, west of 

 Baraga, and as it has been stated, that it is the only outcrop of 

 Silurian limestone in Michigan west of Keweenaw Bay, I think 

 the knowledge of a new locality will be of interest to the readers 

 of your magazine. 



Early last winter Mr. Abner Sherman of Houghton, brought to 

 my office at the Mining School, a specimen of limestone which, 

 he said, was taken from an outcrop near the center of Section 

 7, T. 51, R. 34. Having some doubt as to the limestorte being in 

 place, I decided to visit the location in order to verify the obser- 

 vations of Mr. Sherman. June 4th I started for the locality, in 

 company with Drs. Hubbard and Lane, of the Geological Survey, 

 and Mr. L. A. Wright, of the Mining School. 



The limestone was found to occupy a synclinal basin, the 

 greater part of which lies south of the center of the aforesaid 

 sectioD. The major axis of the fold lies about north 30° east, and 

 the dip varies from 3° to 28°, the steeper dip being northwesterly. 

 The strata exposed will approximate a hundred feet in thickness, 

 and form bluffs, which in places, rise precipitously to the height 

 of sixty-five feet. These bluffs form a higher and a lower terrace, 

 which can be traced for about five hundred paces. The Lake 

 Superior sandstone was seen to dip in conformity with the lime- 

 stone, the two rocks being separated by only a few feet of talus. 



The fossils collected are characteristic of the Lower Silurian 

 (Trenton). Besides brachiopocls, lamellibranchs, gasteropods, 

 corals, crinoids, bryozoa, etc., I found the pygidium of one trilo- 

 bite. 



Advantage of the occasion was taken to visit Limestone Mt. on 

 sections 13, 14, 23 and 24, T. 51, R. 35. Here near the bottom of 

 the limestone series, fossils were collected which correspond with 

 those above mentioned from section 7. Higher up in the series 

 were found characteristic Upper Silurian fossils, probably 

 Niagara. Our observations thus verify those of Mr. W. L. 

 Honnold,* who three years ago, collected Niagara fossils from 

 this location. The finding of limestone outcrops on section 7, 

 makes it quite probable that careful search will reveal others 

 capping high synclinal hills in the sandstone area. 



Michigan Mining School, Houghton, Mich., June 18, 1894. 



4. Etude sur la determination des Feldspaths dans les plaques 

 minces; by A. Michel Levy (Baudry), Paris, 1894, 8°, 70 pp. 

 8 pi. in col. — The appearance of this work is another token of the 

 excellence of the methods of research with which petrography is 

 being supplied. 



We are already indebted to the author for many valuable re- 

 searches on the relations between the optical and crystallographic 

 properties of the feldspar group with special reference to their use 



* This Journal, xlii, p. HO, 171, 1891. 



