November 7, 1884.] 



SCIENCE. 



447 



from a single locality, and are of questionable 

 validit}'. The}' have, however, to be recog- 

 nized in a work like this, and in the want of 

 positive evidence to exclude them ; and it re- 

 mains for future students to determine their 

 true status. 



Late European authorities are here followed 

 in separating the anomalous genera Sphagnum 

 and Andreaea as distinct orders.; while in 

 the Bryaceae, or mosses proper, Schimper's 

 arrangement is in general adopted, with an 

 occasional consolidation of his too numerous 

 tribes and genera, — notably in the case of 

 the genus FTypnum, which, under twenty-eight 

 subgenera, is made to include nearly a fourth 

 of all the species. By several artificial and 

 analytical ke}'s the student is aided in referring 

 his plants to their proper tribes and genera, 

 the characters of which, as well as of the 

 species, are given with sufficient fulness and 

 detail. The synonymy and citation of author- 

 ities, while not numerous, are such as to be 

 of service to the student capable of benefiting 

 by them. The habitat and range within our 

 limits is given under each species, but not 

 always with sufficient definiteness ; and it is 

 rarely that there is any indication that a species 

 is also exotic, except as it may be inferred 

 from the citation of Bruch and Schimper's 

 figures in the i Bryologia Europaea.' The 

 nomenclature, too often a weak point with 

 bryologists, is, on the whole, to be commended 

 as in conformity with accepted rules, though 

 subject to criticism in some cases ; as where 

 the generic names, Ulota, Tetraphis, and 

 Atrichum, are retained in place of the earlier 

 Weissia, Georgia, and Catharinea of Ehrhart. 

 The views of Mueller, Mitten, and Lindberg, 

 when not followed, are in many cases given in 

 the synonymy. 



The publishers have made the book attractive 

 by large, clear type and good paper. Many 

 would doubtless have preferred a somewhat 

 smaller type and thinner paper, by which the 

 bulk of the volume might have been reduced 

 at least one-half. Publishers should remember 

 that the convenience of a ' handbook ' is in- 

 versely as its size. S. W. 



GEOLOGY OF SOUTH-EASTERN 

 PENNS YL VANIA . 



Theses presentees a la Facultedes sciences de Lille uni- 

 versite de France pour obtenir le grade de docteur es- 

 sciences naturelles. Par Persifor Frazer, 

 A.M. Lille, 1882. [6] +179 p., 4 pi. 4°. 



This work is based upon the author's labors 

 as a member of the second geological survey 



of Pennsylvania during the seven 3-ears from 

 1874 to 1881, being essentially a synopsis of his 

 published reports (C 1 , C 2 , C 8 , C 4 ) on Adams, 

 York, Lancaster, and Chester counties. These 

 counties, with the addition of Delaware and 

 Philadelphia counties, which are geologically 

 but an extension of Chester county, include 

 all that part of Pennsylvania south of the belt 

 of triassic sandstone, stretching from the Del- 

 aware to the Susquehanna, and east of South 

 Mountain. 



Professor Frazer recognizes, in the rocks of 

 this limited area, representatives of the four 

 principal divisions of geological time, — the 

 cenozoic, mesozoic, paleozoic, and eozoic 

 eras. The tertiary beds, however, are of no 

 commercial or structural importance, being 

 restricted to a few small isolated patches of 

 marl and lignite. The mesozoic or secondary 

 rocks are, of course, the triassic sandstones, 

 shales, and trap, concerning the limits and age 

 of which geologists are generally agreed. 

 With these exceptions, this is essentially a 

 region of crystalline rocks ; and the interest 

 of this memoir undoubtedly centres in the 

 chronological disposition of these stratified 

 crystallines made by our author, who evinces 

 an appreciation of the difficulties attending 

 any solution of this vexed problem in citing the 

 singular fact that those sections of the United 

 States which are the seats of the densest 

 population and the oldest civilization are 

 precisely those where the opinions of geologists 

 concerning the age of the rocks present the 

 greatest divergence. 



These rocks, and their extension in other 

 states of the Atlantic seaboard, have been the 

 principal battle-ground of American geologists 

 for the last forty years. In all regions the 

 chief difficulties which they present are their 

 structural complexit}^, and the general absence 

 of organic remains. But to these we have 

 added, in the district in question, a topography 

 affording few reliable outcrops of the rocks. 

 The Susquehanna forms a remarkable natural 

 section of this region, crossing the strike of 

 all the formations between the coal-measures 

 and the fundamental gneiss. But even here 

 the exposures are few and poor, although what 

 is definitely known of the succession of the 

 lower formations in Penns} T lvania has been in 

 great part derived from the study of the rocks 

 along this river and the Schuylkill. 



Our author regards these crystalline rocks 

 as belonging largely to the older eozoic forma- 

 tions, and accepts Dr. Hunt's definitions of the 

 Laurentian and Huronian systems, referring 

 to the former the porphyritic and hornblendic 



