138 



SCIENCE. 



[Vol. V., No. 106. 



tion on lithology, not from fault to be found 

 with the treatment of the subject, but because 

 lithology has now become too serious a study 

 to be treated in so compressed a form. The 

 student who uses this book without previous ac- 

 quaintance with the rock-forming minerals that 

 are here briefly described cannot obtain from 

 the forty-six pages given to this section the 

 knowledge that they are intended to give ; un- 

 less, indeed, there is so liberal a supplement of 

 personal instruction as to make the text practi- 

 cally unnecessaiy. We are familiar nowadays 

 with the reaction against the mere verbal teach- 

 ing of physics and chemistry, zoology and 

 botany. The same spirit of reform should 

 exclude brief treatment of lithology from an 

 elementary book on physical geology. And, if 

 the student protests that he wishes to gain at 

 least a superficial knowledge of lithology, let 

 the teacher confidently assure him that there 

 is no such thing, but only a superficial igno- 

 rance. Better admit full ignorance than pre- 

 tend to scanty knowledge, and use the space 

 in the book and the time that would be given to 

 it for fuller discussion of other subjects. The 

 open admission of the author's own lack of 

 expertness in modern lithology, by his accept- 

 ance of a chapter on the igneous rocks from 

 Professor Bonney, is evidence enough that the 

 section in question should not have been in- 

 serted in a book of this title. 



The rest of the work is more satisfactory, 

 because the elements of the subjects that it 

 professes to teach can really be learned from 

 it. It is characteristically British in fact and 

 example, although some illustrations are taken 

 from other countries. Its figures are hardly so 

 good as the}* should be in this day of dry-plate 

 photographs and easy reproduction of pen- 

 and-ink diagrams. The chapter on earthquakes 

 needs a good revision, and a terminology might 

 be improved that allows such expressions as 

 ' mass or weight,' ' ridge or mesa,' using these 

 words apparently as synonymes. But, as a 

 whole, the book gives brief, correct, and well- 

 arranged mention of the more salient geologi- 

 cal facts and theories, under the headings of 

 ' change by internal causes ; ' - surface agencies, 

 destructive and constructive ; ' ' petrology and 

 physiographic geology.' The description of 

 the effects of faulting is exceptionally full ; and 

 unconformity, overlap, and overstep receive 

 more than the usual share of attention. Under 

 fluviatile agencies, Powell's expression, ' base 

 level of erosion,' is accepted as the most fitting 

 to describe this important and commonly neg- 

 lected plane of reference ; and, after definition 

 and illustration, the author pertinently adds, 



that it is mainly because the early advocates 

 of river-erosion neglected to insist on the con- 

 trol which elevation or depression exercised on 

 river-action, that many observers have been 

 unable to believe that rivers have had any sig- 

 nificant share in the excavation of their valleys. 

 There is to our mind an unnecessary scepti- 

 cism as to the subglacial origin of bowlder-clay. 

 The small and now old glaciers, which have long 

 ago swept their beds so clean, afford only im- 

 perfect illustration of what went on beneath 

 the ice-sheet just after its conquest of a land 

 covered with the waste of secular disintegra- 

 tion ; and there is nothing inconsistent in the 

 belief that till was accumulated at one place, 

 while moderate-sized lake-basins were exca- 

 vated at another, as Geikie and Helland have 

 fully shown. The localities selected for illus- 

 tration are so largely English, that the book 

 would require re-making to prepare it for Amer- 

 ican schools. We wish that some of our geol- 

 ogists who are broadly acquainted with the 

 country east and west might undertake the 

 task. 



A TEXT-BOOK OF MICROSCOPICAL 

 PETROGRAPHY. 



At this time, when the interest in micro- 

 scopical petrography is so steadily on the in- 

 crease, the need of a concise, accurate, and 

 recent text-book on the subject is daily be- 

 coming more apparent. That such a one does 

 not exist in English is to be much regretted ; 

 but this very fact will cause information re- 

 garding an admirable one, which has just 

 appeared in Germany, to prove all the more 

 acceptable to geological students. Dr. Hus- 

 sak's book is short and elementary 7 ; but it 

 contains the results, even the most recent, 

 which have thus far been attained by the many 

 workers in microscopical mineralogy 7 and lith- 

 ology 7 , stated in a clear manner. 



The first part treats of methods — optical, 

 chemical, and mechanical — which are now 

 applied to the stud}* of rock-constituents, as 

 well as the general morphological properties 

 which characterize them. Part second con- 

 sists of a tabular arrangement of all the rock- 

 forming minerals, with their characteristic 

 microscopic appearance, chemical reactions, 

 associations, decomposition products, and all 

 other peculiarities which might serve in their 

 accurate diagnosis, arranged in parallel col- 

 umns. This is all given in a very small space ; 

 but the copious and excellent references furnish 



Anleitung zum bestimmen der gesteinbildenden mineralien. 

 Von Dr. Eugen Hussak. Leipzig, 1885. 196 p., 103 figs. 8°. 



