Reviews—Prof. Prestwich’s Geology, Vol. II. 163 
West of England point of view, but there are short accounts of the 
beds in the Midland counties, Lincolnshire and Yorkshire.’ 
Passing on to the Cretaceous chapters, we miss a reference to Mr. 
Meyer’s observations on the “ Punfield Formation,” for these to a 
certain extent tended to destroy its individuality. The various 
divisions of the Wealden and Lower Greensand, however, are 
briefly noticed, and the more marked physical changes are pointed 
out. The unconformity and overlap of the Lower Greensand where 
it rests on the Jurassic rocks in Wiltshire and other parts of the 
country is in reality more pronounced than the word ‘slight’ seems 
to indicate. 
With regard to the Greensand of Blackdown much information has 
been given in papers by the Rev. W. Downes, while Mr. Meyer 
relinquished the opinion that any part of the formation was 
synchronous with the Upper Neocomian (Quart. Journ. Geol. Soc. 
vol. xli. p. 27). 
The account of the Chalk and its origin, together with that of the 
flints, will be read with interest. Prof. Prestwich is of opinion 
“that during the sedimentation of the Upper Gault, Greensand, and 
Lower Chalk, silica, held in solution by alkalies or carbonic acid, 
was introduced in exceptional quantities into the Cretaceous seas by 
rivers and springs, and that it there underwent decomposition in 
presence of some of the sea-salts.” We must, however, refer our 
readers to the work itself for the amplification of these views, the 
author concluding that “it is to the presence of silica in the peculiar 
condition known as soluble silica that the formation of flints is due.” 
The Tertiary strata call for no especial remark. On this subject, 
indeed, our knowledge is most largely due to Prof. Prestwich himself. 
The Lower Bagshot Sands, as noted in a recent paper by the author, 
are grouped with the Lower Eocene on account of their intimate con- 
nection with the London Clay. The Bovey Tracey Beds are discussed 
with the Oligocene Beds, the author remarking that the evidence 
brought forward by Mr. J. S. Gardner to place them in the Eocene 
division is “ by no means conclusive.” 
In the Pliocene chapter the Lenham and St. Erth Beds are duly 
noticed, while the Coralline Crag is described under the name of 
“White Crag.” The Cromer Forest-bed is, however, included in 
the “ Westleton Series,” and mentioned among the Pre-Glacial beds 
of the Quaternary Period. The Glacial beds and associated phe- 
nomena are described at some length, and the author concludes 
“that after the first extreme glaciation, and the formation of the 
Lower Boulder-clay or Till, a great depression ensued, by which 
Central England, Wales and Ireland, were submerged to the extent 
of 1500 to 2000 feet. This led apparently for a time to the inset 
of warm marine currents, and the introduction of a more southern 
marine fauna; but, as the land again rose, and the warmer currents 
were diverted or stayed, colder conditions resumed, and arctic 
1 We should mention that the references to figs. 1 and 2, and 5 and 6 on plate vi.; 
those to 4 and 5 on plate vii.; and again those to 7 and 8 on plate x. are unfortunately 
transposed, 
