118 The Microscope. 



ABSTRACTS. 



Ferruginous Schist and Iron Ores of Lake Superior. — A 

 thorougli microscopic study of the ferruginous schist and iron ores of 

 the Lake Superior region is given by Prof. R. D. Irving, in the 

 October number of the Aniei^icmi Journal of Science. He con- 

 cludes: (1.) The original form of the iron-bearing horizons was that of 

 a series of thinly bedded carbonates interstratified with carbonaceous 

 shales, not unlike the associations of the iron carbonates of the coal 

 measures with carbonaceous layers. (2). By a process of silicifica- 

 tion the carbonate-bearing layers were transformed into various 

 ferruginous rocks, and sometimes the iron was leached out. (3). 

 The iron thus removed was redeposited, making ore bodies, or form- 

 ing the coloring matter of jasper. (4) Where the iron was retained, 

 there may have arisen the actinolitic magnetite schists. (5) The 

 rich ore bodies may have been the result of leaching, of direct oxida- 

 tion of the original carbonate, or may be unusually rich parts of the 

 magnetite schists. The author seems to be well satisfied that these 

 iron ores are not of eruptive origin, though silicification demands the 

 presence of a considerable heat. 



The Effect of Continued Heat on Rocks. — The effect of long 

 continued heat, artificially applied to certain vitreous rocks, like 

 obsidian and pitchstone. has been investigated by Mr. F. Rutley, of 

 the Normal School of Science, whose paper on the subject has 

 recently been published by the Royal Society. Thin sections of the 

 rocks in their normal condition, and after exposure to heat in a glass 

 furnace, have been studied microscopically, and the resulting changes 

 of structure exhibited in a series of illustrations. It is not likely 

 that in nature rocks are ever subjected to absolutely dry fusion, and 

 hence another series of experiments is to be made, with the introduc- 

 tion of water, so as to imitate as closely as possible the actual con- 

 dition of nature. — English Mechanic. 



Extracts From the Note Books or the American Postal Micro- 

 scopical Club. — -To any one who has made sections of limestone 

 fossils, frequently much ciystallized, T need not say that sections are 

 made with as little dirt in the mount as possible, but that little may 

 be much. The sections cannot be removed, but must be mounted on 

 the slide on which they are ground. Prof. Nicholson, now of the 

 College of Edinburgh, Scotland, first suggested and put in practice 

 the study of fossil corals by modern scientific methods, viz., by 



