Reviews—A. J. Jukes-Browne—Building of British Isles. 477 
generally adopted, that the Oxfordian epoch represents the period of 
maximum depression, although he allows that a large part of the 
eastern land was submerged during the formation of the Oxford 
clay. ‘‘ The episode of the Corallian beds,” he says, “‘ marks a time 
when from some cause the deposition of mud ceased over certain 
parts of the sea-bottum, and the water became clear enough for the 
growth of coral reefs.” He concludes that this represents a pause 
in the general subsidence. Such an explanation will only suit some 
districts, because the Corallian limestones, etc., have their argillaceous 
equivalents over considerable areas. We are inclined to think that 
the Oxfordian beds do, on the whole, represent the most extensive 
and regular depression of Jurassic time in our own and neighbouring 
areas, that the Corallian beds indicate, as the author says, a pause, 
but one of irregular distribution, and that the Kimmeridge Clay was 
deposited in an oscillating area—a supposition which can alone 
account for the extraordinary variation in its thickness and character 
within short distances. 
These oscillations at length resulted in the restriction of the 
Jurassic water-spaces, such as must have occurred during the Port- 
landian epoch. This geography is represented in plate viii. The 
Portlandian Sea is open towards the Paris basin, and occupies only 
a portion of the South of England. A strip of water on the coast 
of Lincolnshire and East Yorkshire has an undefined connection with 
a gulf which points towards Germany, and there is the usual water- 
space to the south of the Isle of Man—admitted to be hypothetical. 
It is interesting to note that throughout the first half of Mesozoic 
time, dating from the Permian to the Portlandian, whilst the Atlantic 
is completely ignored, whilst of the North Sea and the English 
Channel there is not the slightest trace, yet the shallow Irish Sea is 
always represented as having been submerged. Certainly a boring 
in this area, if it were possible, should produce most interesting 
results. Permian, Triassic, Liassic, and Oolitic rocks, even to the 
Portlandian, ought there to be found in undisturbed sequence. 
The remaining periods must be considered briefly. Omitting the 
stage of the Purbeck-Wealden, we find, when marine deposits once 
more take place, the two principal water-spaces of the Portlandian 
epoch, somewhat modified, are now connected by narrow straits in 
the East Midlands. This arrangement represents the Aptien (Lower 
Greensand) stage of the Lower Cretaceous (plate ix.). All else is 
land. Even the bed of the Irish Sea is at length brought up to 
day, and might thus lose some of its earlier Mesozoic deposits. 
But, since coming events cast their shadows before, a dubious out- 
line of the Atlantic for the first time appears off the north-west 
coast of Ireland. This scene may be taken to represent the last 
stage of Mesozoic geography before the great submergence which 
ultimately brought the waters of the Chalk Sea over the area of the 
British Isles. The author does not venture to portray the great 
consummation, but plate x. represents the geography of the period 
when the basal sediments of the Chalk. e.g. Gault, Upper Greensand, 
etc., were creeping over England. ‘The laying down of the probable 
