Proceedings of the British Association. 249 



mingled with some tropical forms. Mr. Forbes had mentioned a 

 similar admixture taking place on the shores of the Egean at the pre- 

 sent day, the insects of the mountains being washed by floods into the 

 sea mingled with those requiring a higher temperature. And as there 

 was evidence of rain having fallen in the period of the new red sand- 

 stone, in all probability it had continued in the lias. During all the 

 oolitic period the land appears to have continued to rise towards the 

 west, so that the oolitic strata were deposited in a constantly dimi- 

 nishing area ; half were already above water, while the upper beds 

 were depositing, and all the high land which was not already destroyed 

 was above water. Denudation by the sea did not therefore further 

 progress at this period in what is now South Wales. During the 

 cretaceous period a partial depression took place, and the sea may 

 again have crossed the Severn, and washed against the old coats ; 

 Mr. Ormerod has found chalk flints abundantly on the banks of the 

 Severn near Chepstow. Again a rise took place before the deposi- 

 tion of the London clay, but the disturbances by which the chalk was 

 elevated were comparatively of a tranquil nature. After the deposi- 

 tion of the London clay, Mr. Ramsay therefore considers there 

 may still have been mountains in Wales of the great height already 

 indicated, and to remove these the land must have again gone 

 down to a depth at least corresponding to the height of the highest 

 hills which now exist in Wales ; on the tops of some of these, as 

 on Moel Tryfan, there is drift, with recent marine shells, at a height 

 of 1,500 feet. The whole change from tins condition to the present, 

 must have been effected during the tertiary period, and part of it 

 immediately prior to our own. 



Prof. Sedgwick reviewed the evidence afforded by Mr. Ramsay's 

 communication of the successive changes which had taken place on 

 the surface of the earth in the most remote periods ; he alluded to 

 the lapse of time required for the accumulation of such vast masses 

 of shingle and sediment formed of the destruction of pre-existing 

 rocks, for the growth of coral-reefs, and for the formation of the coal- 

 measures from the accumulated vegetation of a long succession of 

 peats and peat-bogs. During the progress of these physical changes, 

 the population of the ancient sea had been repeatedly destroyed and 

 renewed, not suddenly, but gradually and in accordance with the opera- 



