194 PHYSICAL GEOLOGY. 



4. MISCELLANEOUS. 



Croft, Thomas. The Self-propagating Nature of Centrifugal Porce 

 as it aifects our Earth and other Portions of our Solar System. 

 Pp. 20. 8vo. Papeete {Tahiti). 



Part 1. Geological Yiew, pp. 1-16. 



Croll, T. Climate and Time in their Geological Belations. A 

 Theory of Secular Changes of the Earth's Climate. Pp. xvii, 577 ; 

 8 plates. 8vo. London. 



Starts with the thesis, that " climatic agents have been the principal 

 factors concerned in that long succession of events and changes which 

 have taken place since the solidification of the earth's crust." The 

 distribution of heat over the globe by Ocean Currents is then discussed ; 

 and it is shown that they carry the surplus heat from tropical regions 

 to temper the severe climate of high latitudes. In Chaps. 4, 5 the 

 eiFect of changes in the eccentricity of the earth's orbit combined with 

 the Precession of the Equinoxes and the Ee volution of the Apsidal 

 Line is discussed, and it is shown tbat during a period of high eccen- 

 tricity a Glacial Period will be produced in that hemisphere whose 

 winter occurs in Aphelion. Chaps. 6-14 attack the Gravitation 

 Theory of the cause of Ocean Currents, and maintain that these currents 

 are due to the action of prevalent winds. Chaps. 15, 16 give evidence 

 for warm interglacial periods ; Chaps, 17, 18 for former glacial periods 

 in the earth's history. Chap, 19 contains an attempt to determine the 

 absolute date of the last glacial epoch ; and Chap. 20 explains a method 

 of employing the rate of subaerial denudation as a measure of geo- 

 logical time. In Chap. 21 it is sbown that it is probable that the sun 

 was formed by the collision of two bodies, the amount of heat produced 

 by the condensation of a nebulous mass, not originally possessed of 

 heat, being believed to be insufficient for the needs of geology. Chap. 

 22 discusses a means of arriving at an estimate of the mean thickness 

 of the sedimentary rocks. Chaps, 23, 24 treat of the change in sea- 

 level which would be produced by the shifting of the earth's centre of 

 gravity by a polar ice-cap. Chap. 2b deals with the effect which a 

 change in the Obliquity of the Ecliptic would have on Climate and the 

 Level of the Sea ; when, during a period of high eccentricity, the obli- 

 quity reaches its maximum, the hemisphere under glacial conditions 

 would have the severity of its climate somewhat lessened, and the 

 equable climate of the other hemisphere would be rendered still more 

 genial. In Chap. 26 it is maintained that Coal is an Interglacial 

 formation. Chap. 27 deals with the path of the Ice-sheet in N.W. 

 Europe, with special reference to the Boulder Clay of Caithness; 

 Chap. 28 with the N. of England Ice-sheet and the dispersion of 



