230 GEOLOGY. 



powers, who familiarized themselves with the objects that they studied 

 and learned to recognize them. The great step in advance, for the aid 

 of the new students, was made by Eosenbusch, who applied the optical 

 l)rinciples discovered and analyzed by Des Cloizeaux to the examination 

 of microscopic crystals as seen in extremely thin sections of rocks. Des 

 Cloizeaux Laving deduced the ojitical properties of all commonly occur- 

 ring minerals, these same proijerties were sought in the microscopic 

 sections, and the determination aided by a microscope adapted to the 

 purpose. The limited knowledge of minerals in general and the lack of 

 knowledge of optical jtroperties, had been the reason why the suggestion 

 of Cordier, who in 1816 recommended the employment of the microscope 

 in geology, had never been to any extent followed. During these last 

 years a xeiy respectable proportion of the geological literature published 

 in Germany has been devoted to microscopical lithology. The study 

 has reached a high state of perfection in France, but less of consequence 

 has ever been done by the Euglish or Americans. These few words 

 may serve as an introduction to the progress of the past two years. 



As one mark of interest in this subject, the change in the editorship 

 of perhai)S the most important geological magazine should be noted. 

 The '■'■ Jahrhiich fitr Mineralog^ie und PalcE07itologie,''^ which for a half 

 century had been conducted by Leonhard, and later by Leonhard and 

 Geinitz, has now passed into the hands of a trio of editors, one of whom 

 represents mineralogy (Professor Klein, of Gottingen), one paheoutology 

 ( Professor Benecke, of Strasburg), and one of whom represents inor- 

 ganic geology, and to this office Professor Eosenbusch, of Heidelberg, 

 the eminent lithologist, was called. These gentlemen have organized a 

 corps of assistants in the various lands, and aim to make this periodical 

 a general exponent of progress in the subjects that they cover. They 

 have issued two volumes during the past year, instead of one as hereto- 

 fore, and it is certainly very pleasing to the students to have recourse 

 to such an encyclopsedic work now that mineralogical and geological 

 literature is so extensively published in a multitude of often inacces 

 sible magazines and proceedings of societies. 



The first treatise that has ever been written upon lithology in the 

 English language has apjicared. There have heretofore, it is true, been 

 translations, notably of von Cotta's work, and little chapters in geology 

 have been devoted to lithology ; but von Cotta's book is old, and the 

 cliapters in geological works laid claim to few pretensions. The new 

 book is by Frank Eutley, and was published in London. To be sure, 

 it is very poor, and is mostly abstracted from the writings of Germans, 

 but it is beginning to be improved ujjon. 



In this country, within the past two years, interesting miscroscopic 

 lithological work has been done by gentlemen connected with the Wis- 

 consin geological survey, and some initiative attempts have been made 

 upon rocks in Pennsylvania and Massachusetts. I have already referred 

 to the first, and the latter are hardly in a condition to be reviewed yet. 



