E. MINERALOGY AND GEOLOGY. . 83 



this melted sulphur was then poured into a deep wooden ves- 

 sel, and, in cooling, a crust was formed upon the surface. A 

 hole was made in this crust and kept open, and through this, 

 as the congelation of the sulphur proceeded, eruptions of 

 melted sulphur, with exhalations and explosions of steam, 

 took place at regular intervals ; and after a short time a min- 

 iature volcanic cone was formed, with all the characteristics 

 of a volcano made by successive lava streams. 12^1,1870, 

 Bee. 29, 179. 



THE MICROSCOPE IN GEOLOGY. 



The microscope has rendered its aid to an immense num- 

 ber of branches of physical investigation in turn, and quite 

 lately its value to the geologist has been shown by the re- 

 searches of Mr. David Forbes and others. Mr. Alport, in a 

 recent communication, gives, as the result of many hundreds 

 of sections of rocks and minerals, the assurance, first, that the 

 mineral constituents of the melaphyres and other fine-grained 

 igneous rocks may be determined thereby with certainty a 

 result which has not been attained by any other method of 

 examination. Second, that the mineral constituents of the 

 true volcanic rocks and of the old melaphyres are generally 

 the same. Third, that the old rocks have almost invariably 

 undergone a considerable amount of alteration, and that this 

 change alone constitutes the difference now existing between 

 them and the recent volcanic basalts. 5 A, Oct., 1870, 430. 



ANDREWS OX THE CHRONOLOGY OF AMERICAN LAKES. 



Professor Andrews, of Chicago, in a memoir published by 

 him upon " The North American Lakes (Michigan and Huron 

 especially), considered as chronometers of post-glacial time," 

 comes to the following conclusion in regard to their history 

 and chronology, assuming that their formation took place 

 during or at the close of the drift period: "1. The upper 

 beach of the lakes began to form immediately after the bould- 

 er-drift period, and continued to accrete for about nine hun- 

 dred years. No animal fossils have yet been found in it. 2. 

 The waters then fell suddenly to about their present level, 

 where they remained till a thin bed of peat accreted on the 

 marshy slope vacated by the waves. Data are not at pres- 

 ent available for a calculation of this low-water period, but 



