Review of Recent Geological Literature. 261 
British geologists, is the origin of the shell-bearing drift deposits 
at high levels on Moel Tryfaen, and in other parts of northern 
Wales, Cheshire and Lancashire, which Lewis attributed, follow- 
ing Belt and Goodchild, to transportation by an ice-sheet which 
moved from Scotland and northern Ireland southward across the 
bed of the Irish sea. The work of glacial investigation by Lewis 
in England, which was left unfinished by his lamented death, has 
been taken up with earnestness by many workers under the name 
Northwest of England Boulder Committee, of which Prof. Perey 
F. Kendall, of Stockport, Eng., is secretary. In a paper before 
the Boston Society of Natural History, March 2, Prof. G. F. 
Wright described the work of this committee, and the admirable 
generalization of Prof. Kendall, now fully demonstrated, that 
wherever the shells, mostly fragmentary, are found in the drift at 
great elevations, there are also boulders from rock outcrops north- 
ward of the Irish sea, brought by the ice-sheet which gathered 
these shells from the seabed. The ‘‘great submergence” of parts 
of Great Britain, which was supposed to have taken place during 
an interglacial epoch, is thus shown to be a needless and erroneous 
assumption, 
REVIEW OF RECENT GEOLOGICAL 
LITERATURE. 
The Cause of an Tce-Age, by Sir ROBERT BALL, RoyAL ASTRONOMER OF 
IRELAND. D. Appleton & Co, 1891, pp. 180. 
The discussion of the cause of an Ice-Age is prefaced in this little 
volume, by a brief statement of the records left by the ice, and by a 
statement of the nature of glacial and “genial” periods As indicated 
by the title, the vital part of the volume is the discussion of the cause 
of glacial climate. This discussion consists of a brief exposition of the 
astronomical hypothesis,—with amendment. Sir Robert’s amendment 
to the astronomical hypothesis, as it has commonly been stated, may best 
be given in his own words, set in contrast to the general statement of the 
effect of varying eccentricity of the earth’s orbit given by Herschel, and 
quoted by the author (p. 116). “ ‘Supposing the eccentricity of the 
earth’s orbit was very much greater than it actually is, the position of 
perihelion remaining the same, it is evident that the characters of the 
seasons in the two hemispheres would be strongly contrasted. In the 
northern we should have a short but very mild winter, with a long but 
very cold summer, 7. ¢, an approach to perpetual spring, while the 
southern hemisphere would be inconvenienced, and might be rendered 
