July 13, 1883.] 



SCIENCE. 



49 



must be undertaken deliberately, planned by 

 human intelligence, and achiev«i through hu- 

 man cflTort. 



The author discusses, in a broad and philo- 

 sophic manner, a great body of questions in 

 which civilized, man is deeply interested. He 

 has therefore written for a wide reading ; and 

 happily his style, in its essential character- 

 istics, will not repel those to whom it is pre- 

 sented. 



GEOLOGY OF SOUTHERN PENXSVL- 

 VANIA. 



Second geological survey of Pennsylvania. — Report 

 of progress T-. — The geology of Bedford and 

 Fulton counties. Bv J. J. Stevensox. Harris- 

 burg, Survey, 1882." 15 + 382 p., 2 maps. 8°. 



PuoFEssor Stevessox has made a detailed 

 survey of the district, which has led to but few 

 material changes in the map of the first survey. 

 The descriptions of the structural geology are 

 careful, plain, and easily understood ; and the 

 second part of the report, consisting of a d.aj'- 

 book of observations along the roads, with ref- 

 erence to outcrops, mines, and quarries, will 

 doubtless prove very useful. 



It is well that Professor Stevenson has not 

 completely neglected paleontology in his de- 

 scriptions of the various form.ations ; but this 

 feature of his report is capable of much im- 

 provement, only about si.xty species being 

 cited as occurring in a section that extends 

 from the upper coal-measures to the calcifer- 

 ous. The value of his determinations, and 

 the scientific interest of his work, would have 

 been much increased, if care had been taken 

 to collect and determine the fossils found in 

 each group, and lists of them published, 

 together with the localities in which they oc- 

 curred. It is not meant to infer that Profes- 

 sor Stevenson's determinations are incorrect, 

 ■ but siinpl\- that he gives no evidence in sup- 

 port of them. For instance : he says, " Some 

 of these lavers contain fossils which are dis- 



tinctly Chemung, none whatever of Portage 

 type being present ; but, owing to the weath- 

 ering, the forms can be identified onlj* generi- 

 c.ally." The writer does not think he is alone 

 in doubting whether there are any fossils which 

 are distinctively Chemung. At any rate, it 

 would be interesting to know what these gen- 

 era are. He mentions no fossils in his Hudson 

 River group, and in the Trenton mentions only 

 three forms, which are also very common at the 

 top of the lower Silurian. The director of the 

 survey, in his letter of transmittal, makes 

 the following curious remark, which seems to 

 indicate a peculiar conception of the objects of 

 paleontologj-. He says, " Paleontologists will 

 find it an easy task to copy out from the index, 

 separately, the whole list of fossil names, and 

 arrange them afterwards to suit their own pur- 

 poses." Certainly, paleontologists do not want 

 to arrange fossils to suit themselves, but to 

 find out how nature has arranged them. The 

 two maps accompanying the report are of very 

 indift'erent quahty, as it is difficult, especial!)- 

 over the Broad Top area, to follow on the maps 

 the descriptions in the text. Mr. Stevenson 

 disclaims responsibility for several things in 

 them, which may account for the discrepancies 

 between the text and the maps. Professor Les- 

 ley seems to think tiiat the maps maj- be easily 

 followed by a person familiar with the country ; 

 but the maps should have been constructed so 

 that others, also, may be able to understand 

 them. He seems to apply preconceived no- 

 tions of orography, whether it agrees with the 

 geology as studied in the field or not ; and, if 

 the responsibility of preparing the maps rested 

 with the same [lerson who has done the field- 

 work and prepared the text, the result would 

 probably be more intelligible. Mr. .Stevenson 

 mentions a bed 19.j feet above the Pittsburg 

 coal. This would apparently belong to the 

 upper series, considered Permian in other re- 

 ports of the survey ; but tiiis does not appear 

 to be represented anywhere on tiie map. 



WEEKLY SUMMARY OF THE PROGRESS OF SCIENCE. 



ASTRONOMY. 

 Ziclipses of Jupiter's satellites. — Cornu pro- 

 poses to observe these eclipses photometrically, cora- 

 paritig the light of the satellite during the time 

 while It Is entering or emerging from the shadow 

 with that of an artificial satellite visible in the same 

 field, and made to vary in brightness at pleasure by 

 an adjustable ' cat's eye,' so called. lie shows that 

 the moment when the light of the satellite is half 



that of its unobscured condition is the one which 

 can be most accurately determined, and urges that 

 the photometric observations should be so arranged 

 as to give an automatic record. Admiral Mouchez 

 has authorized the application of the necessary ap- 

 paratus to one of the large equatorials of the Paris 

 observatory. 



M. Cornu does not seem to be aware that a very 

 similar, but really more precise, method of observa- 



