Intelligence and Miscellaneous Articles. 571 



matters, this text-book treats of — Division I. — (1) theEarth's origiu 

 and the Nebular Hypothesis. (2) Igneous action ; internal heat. 



(3) Volcanoes aud volcanic rocks ; intrusive and plutonic rocks. 



(4) Metamorphism of rocks. (5) Earthquakes, and earth-movements. 

 Division II. (6) Aqueous action ; its results in forming strata 

 derived from rocks denuded by rain, rivers, frost, snow, ice, and 

 glaciers. (7) Climate ; its changes and effects. Division III. (8) 

 Life; fossils. (9) Stratigraphical Geology; the successive groups 

 of strata and their fossils. Division IV. (10) Petrology ; structure 

 and conditions of strata and other rock-masses ; mineral veins ; 

 mineralogy ; crystallography. (11) The classification and methods 

 of recognizing aud distinguishing minerals and rocks. 



The fourth Division or Section has been added to this edition, 

 " embracing all the more recent requirements of the South- 

 Kensington Syllabus, which now includes under the name of 

 ' Geology ' many topics which were formerly confined to Mineralogy 

 and Crystallography. The new matter comprises chapters on rock- 

 forming minerals, their composition, distribution, characters, and 

 the methods of their identification ; on crystallography ; on volcanic 

 and plutonic rocks, and the microscopic examination of rocks." 



Further chapters give a glossary or instructive explanation of 

 some technical terms relating to common and important pheno- 

 mena met with by the geologist ; also a table of the range in time 

 of important fossil genera (this will bear improvement) ; appendix 

 on Geological Surveying ; and some examination-papers set at 

 South Kensington in 1895-98 ; there is also an index. 



This is one of " Murby's Science-and -Art-Department Series of 

 Text-books " ; and doubtless it is far better, in both construction 

 and contents, than many of the small manuals of geology that are 

 in the hands of students ; and it rivals in value some of the more 

 costly text-books. Besides the good arrangement of the manifold 

 aspects and evidences of the science, the statements and description 

 are clearly aud tersely given ; the leading words are well distin- 

 guished by proper types in the text; and the technical terms are 

 etymologicallv explained at one place or another (but at page 67 

 " strechan, the stretch," should be sirechen, to stretch). 



The letterpress and, in some cases, the woodcuts are not clearly 

 printed. The zoologist might easily find fault with some oi: the 

 figures of, and references to, the lower animals : there are some 

 misprints, as " Syenctic'' ; siliceous rocks, at p. 78, are not at all 

 well defined ; and calcite is omitted from the hexagonal system at 

 p. 198 ; there are several slips in the latinity, such as "folia" 

 instead of folium, a leaf ; and the false concord of Echinoidea 

 regulares et irregulares ! Nevertheless this is a good aud useful 

 text-book, and we recommend it for use in schools and colleges. 



LXIV. Intelligence and Miscellaneous Articles. 



A NEW COMBINATION OF WHEEL-GEARING. (SECOND 

 COMMUNICATION*.) BY J. J. TAUDLN CHABOT. 

 1. rPHE teeth of the wheels of the model described iu my pre- 

 vious communication forming helices, or sere w-lines, the 

 constituent wheels themselves are divisible into two classes accord- 

 ing as the screws are left-handed or right-handed. 



* See Phil. Mag. vol. xlvi. p. 428 (Oct. 1898). 



