December 24, 1900] 



SCIENCE 



929 



The total effect of the parasite has scarcely 

 more than 1 per cent, of the efficiency claimed 

 for it in the publication under consideration, 

 even though this is figured on a 40-fold in- 

 crease instead of 25-fold. In every particular 

 the assumptions upon which the above table is 

 based are more favorable for the parasite than 

 the experimental data presented by Mr. 

 Hunter justify. And, moreover, the efficiency 

 of the parasite does not increase by any such 

 proportion as is generally assumed, the weekly 

 averages only varying from each other by 

 a small fraction, showing that years would 

 have to elapse before the parasite would reach 

 the efficiency supposed to be attained in 

 twenty-five days or a month. 



Of course, other factors enter into the prob- 

 lem, but the point that this calculation demon- 

 strates is that these other factors are so much 

 more important that, as compared with them, 

 the work of the parasite is a negligible factor. 



As corroborative evidence the author quotes 

 Professor Marehal's account of the efficiency 

 of the Australian ladybird against the cottony 

 cushion scale. It may be instructive to state 

 that during the last eighteen years this sup- 

 posedly suppressed scale insect has figured as 

 largely in the correspondence of the entomo- 

 logical department of the University of Cali- 

 fornia as any scale existing in the state, and 

 that on the university grounds and in the sur- 

 rounding region it is now and has been all 

 these years the most injurious scale insect 

 present with the possible exception of the 

 black scale. 



Nearly all previous discussions of the effi- 

 ciency of parasites or predaceous insects have 

 been records of impressions instead of the pres- 

 entation of experimental data. This author 

 has accumulated a splendid lot of data, but 

 has not used it. Like the others of us, he has 

 been so impressed with the evidence he saw in 

 the form of innumerable plant-louse mummies 

 that he failed to grasp the importance of 

 other conditions, probably largely meteoro- 

 logical, which might have caused the disap- 

 pearance of the lice equally as soon had there 

 been no parasites present. Aside from this 

 one question of interpretation the work will be 



of great value to subsequent students of para- 

 sitism. C. W. WOODWORTU 

 U.XIVEBSITY OF C.VI.IFOR.XIA 



Geology of the City of New York. By L. P. 



Gr.\tacap. Third edition. 8vo, pp. x + 232, 



65 figs., 4 maps. New York, Henry Holt 



and Co. 1909. $2.50. 



Gratacap's " Geology of the City of New 

 York " was originally issued in 1901 as a 

 pamphlet of 82 pages, specially designed for 

 teachers of science, for pupils in the schools 

 of the city and for the general reader to whom 

 the metropolitan district furnished an attract- 

 ive field of observation and study. The Amer- 

 ican Museum of Natural History conducts 

 most commendable series of lectures for the 

 teachers of the city and the manual found in 

 them a constituency greatly needing just such 

 a work. With the second edition the text was 

 expanded to 119 pages, and now with the third 

 the size of page is reduced from royal octavo 

 to the more convenient octavo size and is 

 expanded to embrace the latest results of study 

 in the district. Practically a new book has 

 been prepared. 



The work opens with a general introduction 

 intended to place the reader in command of 

 the facts of stratigraphical classification, and, 

 since the area is a metamorphic one, with the 

 general principles and processes of this branch 

 of geology. Manhattan Island is then de- 

 scribed in detail; its topography, its rocks, its 

 waterways, its minerals, etc. The boroughs of 

 Brooklyn and Queens are next treated in a 

 similar but much less detailed manner. Being 

 covered with glacial drift throughout almost 

 all of their area they furnish fewer rock ex- 

 posures. The borough of the Bronx, although 

 nearly as large as Manhattan and of similar 

 formations, receives but a brief mention of 

 four pages, and the borough of Richmond or 

 Staten Island about four times as much. The 

 evidences of glaciation in and about Greater 

 New York are then taken up in the concluding 

 pages. 



The work contains a great deal of valuable 

 record that will prove serviceable to engineers 

 and contractors as well as to teachers and 

 those with a popular interest in science. There 



