172 CIMOL1OSAURUS RtCHARDSONI. 



estuaries, and rivers. With one or two doubtful exceptions, 

 not a single Mesozoic species passed up into the Tertiary 

 strata ; the numbers of the new genera and species, greatly exceeding 

 those of the previous age. Western Europe at this period had four 

 considerable seas instead of one as now the Anglo-Parisian, the 

 Pyrennean, the Mediterranean, and one which covered the western 

 parts of France from Normandy to Nantes. As the chalk rose 

 above the sea and underwent extensive denudation, a material 

 diminution of temperature resulted, mainly through alterations of 

 the ocean currents, which occasioned a disastrous result upon 

 reptile life. During the deposition of the oolitic beds there was 

 a complete uniformity, for, although occasional subsidences 

 occurred, as shewn by the Oxford and Kimmeridge clays, 

 with evidences of tide-level and shore conditions, no great 

 or important break occurred. At the commencement of 

 the Cretaceous age, on the other hand, there was a gradual 

 submergence of land, accompanied by a considerable 

 extension of the sea-area. The marine beds of Punfield, near 

 Swanage, which rest upon the great fresh-water deposits of the 

 Hastings sands, are a good illustration of this initiatory change. 

 Its effects are remarkably shown in the Vale of Blackmore, where 

 there is a great overlap or covering over of the upper oolitic beds 

 by the chalk. The Hastings sands, Purbeck beds, and 

 Portland strata are hidden, causing an apparent unconfor- 

 mity of the beds, as if the Lower Greensand had succeeded the 

 Kimmeridge clay directly, without first covering over the 

 intervening beds. Another subsidence and consequent invasion of 

 the sea occurred during the deposition of the Upper Greensand, 

 which spread itself over the oolitic formations as it passed on 

 westwards, finally resting on the Trias of East Devon. These 

 changes materially affected the climate and temperature of those 

 parts which came under their influence, especially through the 

 alteration of ocean-currents. What would the climate of the greater 

 part of Europe be, if the Gulf Stream was stopped or deflected ? 

 The Atlantic would be deprived of one-fifth of the amount of heat 



