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The Cretaceous seas were probably comparatively shallow; this was certainly the case where the deposits are sandy, and in the regions occupied by the hippuritic fauna. Much discussion has taken place as to the depth of the chalk sea. Stress has been laid upon the resemblance of this deposit to the modern deep-sea globigerina-ooze; but on the whole the evidence is in favour of moderate depth, perhaps not more than 1000 fathoms; the freedom of the deposit from detrital matter being regarded as due to the low elevation of the surrounding land, and the main lines of drainage being in other directions. Sandy and shore deposits are common throughout the system in every region. Besides the Weald, there were great lacustrine and terrestrial deposits in N. America (the Potomac, Kootenay, Morrison, Dakota and Laramie formations) as well as in N. Spain, and in parts of Germany, &c. The general distribution of land and sea is indicated in the map.

Earth Movements and Vulcanicity.—During the greater part of the Cretaceous period crustal movements had been small and local in effect, but towards the close a series of great deformative movements was inaugurated and continued into the next period. These movements make it possible to discriminate between the Cretaceous and Tertiary rocks, because the conditions of sedimentation were profoundly modified by them, and in most