Geology and Mineralogy. 63 



Report of Progress in the Venango Co. District ; by John F. 

 Carll. Observations on the Geology around Warren ; by F. A. 

 Randall. Note on the Comparative Geology of Northimstern 

 Ohio and Pennsylvania and Western JVew York ; by J, P. Les- 

 ley. 128 pp. 8vo, with wood-cuts and maps. 



Report of Progress in the Laboratory of the Survey^ at Harris- 

 burg ; by Andrew S. M'Creath. 106 pp. 8vo. 



Prof. Prime gives in his report a brief account of the topography 

 and geology of the district under examination, and of the rocks 

 with which the limoiiite ores are associated. These rocks are 

 stated to be of the raagnesian limestone series — that is, Lower 

 Silurian beds of the age of the Calciferous sandrock, and the 

 Chazy, Birdseye and Black River limestones. Mr. Prime says : 

 "The great mass of this formation is dolomite; but there occur 

 one and possibly more beds of hydro-mica (or daraourite) slate 

 intercalated in it. The limonite ore always accompanies the 

 hydro-mica slate, and with it there is often clay from the decora- 

 position of the slate. The following are three out of five analyses 

 of this slate from Lehigh Co.: 



From the amount of the potash in the first analysis (by Dr. 

 Genth), Mr. Prime calculates the amount of damourite present 

 (with free silica, etc.) to be 55-40 p. c. ; in the second (by Mr. S. 

 Castle), 49-70 p. c. ; in the third (by Uv. P. G. Salom), 53-02 p. c. 

 This hydro-mica slate, with often associated limonite beds (as a 

 result of alteration), extends, as Mr. Prime observes, from Ver- 

 mont to Alabama, showing thus a long range of Lower Silurian 

 rocks in the eastern mountain region of North America.* 



The report describes fuither the mines and ores, and gives many 

 analyses. It is followed by a note from the State Geologist, 

 making some explanations with regard to the equivalency of the 

 Pennsylvania formations, and remarking on some topographical 

 changes the country has undergone. Mr. Lesley goes outside of 

 his field in his closing remarks, and states — what is sustained as 

 yet by no adequate stratigraphical evidence — that the " Green 

 Mountain system of Vermont" and " the White Mountain system 

 of New Hampshire," are, like "the Laurentian Mountains of 

 Canada," older than the Potsdam ; and that the Green Mountain 

 system, one of these " three great mountain systems of the north," 

 is Huronian. The observations by Mr. Prime in Pennsylvania, 

 above-mentioned, and the parallel facts in the Green Mountain 

 system to which he draws attention, all point as regards the 

 Green Mountains in the opposite direction. The writer has 

 studied stratigraphically the Green Mountain region from Con- 



