526 



SCIENCE. 



[N. S. Vol. III. No. 66. 



On many accounts the report of Dr. Clarke 

 describing the geologic structure of a portion 

 of Chenango county is one of the most impor- 

 tant of these contributions, since it considers the 

 correlation of the rocks for a part of the State 

 concerning which great uncertainty and diflfer- 

 ence of opinion have prevailed. The plate at 

 the beginning of the article gives a clear idea 

 of the character of the sandstones and shales 

 at the base of Vanuxem's Oneonta sandstone, 

 while the figures bring out nicely the lithologic 

 and stratigraphic features of the various sec- 

 tions, which are carefully described by the 

 author and are accompanied by accurate lists of 

 the species of fossils found in the various beds. 

 In the lower exposures, near Norwich, Dr. 

 Clarke found abundant Hamilton fossils ; above 

 these Hamilton species also, but with them 

 specimens of Spirifer mesastrialis, Actinopteria 

 zeta and a few other species which occur in the 

 ' Ithaca group, ' while in the upper part of the 

 shales and sandstones, below the Oneonta sand- 

 stone, fossils are very scarce. 



The formations of the Middle and Upper 

 Hamilton of central and western New York are 

 usually given in ascending order as the Marcel- 

 lus shale, Hamilton sandstone with the Tully 

 limestone at the top, Genesee shale. Portage for- 

 mation (which in central and eastern New York 

 is partly replaced by the ' Ithaca group ' and 

 Oneonta sandstone), and Chemung formation. 

 These formations form the Hamilton and Che- 

 mung series, the line of separation usually be- 

 ing drawn at the top of the Genesee, although 

 some authors prefer to place it at the base of 

 the Tully limestone. 



The Genesee shales and Tully limestone form 

 a marked horizon across western New York, 

 but they disappear in going eastward and are 

 not clearly known east of the Chenango valley. 

 In this eastern area Hamilton fossils, with the 

 addition of a few species found in the ' Ithaca 

 group,' occur in the bluish shales and sand- 

 stones underlying the Oneonta sandstones, and 

 whether these deposits belong in the Hamilton 

 formation, or are above the horizon of the Gen- 

 esee shale and Tully limestone, has been a 

 greatly disputed question. 



Dr. Clarke found in the western part of Che- 

 nango county that the Hamilton fauna with 



Spirifer mesastrialis, ' and of quite the same 

 character as that of the lower beds at Norwich,' 

 is clearly and unmistakably above the Genesee 

 shales. Consequently it will be readily seen 

 that this work is of great value in accurately 

 determining the line of separation between 

 the Hamilton and Chemung series in central 

 New York. In passing it may be stated that 

 this conclusion agrees with the writer's inter- 

 pretation of the section near Smyrna, twelve 

 miles north of Norwich, which is at the most 

 eastern unquestioned exposure of Tully and 

 Genesee. 



The final settlement of difficult questions of 

 this nature in correlation — and there are many 

 in the United States — will be obtained by care- 

 ful field study of a typical region by a geolo- 

 gist familiar with its paleontology and also 

 versed in stratigraphical geology. 



A preliminary copy of the Geologic Map of 

 New York is now passing through the press, 

 and the above and later work of Dr. Clarke, as 

 well as that of other assistants, will be of great 

 value in revising this map upon which the vet- 

 eran State Geologist, Prof. James Hall, has 

 been actively engaged for so many years. 



C. S. Peosser. 



Computation Rules and Logarithms. S. W. HoL- 

 MAN. Macmillan & Co., New York. $1.00. 

 Prof. Holman's book is the outgrowth of sev- 

 eral years' experience with large classes and 

 is sufficient for most of the computations oc- 

 curring in engineering, physics and chemistry. 

 The tabular matter consists of a variety of five 

 and four-place tables, together with modern 

 values of important constants. The introduc- 

 tion, which comprises one-third of the book, is 

 of great value, its chief object being to teach 

 students how to get results of any desired de- 

 gree of accuracy without wasting time and labor 

 in the manipulation of useless figures. For in- 

 stance, the H. P. which can be transmitted 

 safely by a certain wrought-iron shaft is 2-^« 

 1.3643. 10000 •300/6336000. How many places 

 of logarithms are to be employed, if the compu- 

 tation-error is not to exceed one per cent."? By 

 one of the author's rules it is instantly decided 

 that four-place logarithms will give ample ac- 

 curacy. One of the devices on which stress is 



