128 Proceedings of the British Association. 



detached Silurian districts presenting particular changes and modifi- 

 cations, arising from difference of depth, and the variety of currents, 

 and chemical combinations in the sea in which they were formed ; in 

 consequence of this variety of physical condition there was a corres- 

 ponding diversity in the traces of organic life in each situation. 

 The particular circumstances which had given the remarkable suc- 

 cession of organic life in Shropshire had not obtained in Pembroke, 

 where the same series of organic forms had continued from the lower 

 to the upper Silurian period.-r-The President said, he was convinced 

 that future examinations would confirm, not shake, his confidence in 

 the general accuracy of the results which had been obtained by 

 geological investigation. The present question was only whether 

 there should be one chapter instead of two — not whether they should 

 break up the great authentic facts of their history. In the north of 

 England and in North Wales the division between the upper and 

 lower Silurian rocks was as distinctly marked as at Malvern and in 

 Shropshire ; but the subdivisions did not exist, because the physical 

 conditions under which each was developed were altogether different. 

 It was probable that species would be found to have a wider range 

 than was at first supposed, but as to the corals of the Silurian system, 

 the Wenlock species certainly did not make their appearance in the 

 calcareous beds of the Caradoc series where similar conditions pre- 

 vailed. He asserted that in no instance had general conclusions been 

 shaken by subsequent observations ; and he believed that whatever 

 alterations and minute adjustments might take place, the great 

 fundamental principles of the science and the grand subdivisions 

 already introduced into its history would not be upset, but extended 

 and confirmed by future inquiry. Sir H. De la Beche confirmed Mr. 

 Phillips's remarks upon Pembrokeshire, stating that in Marloe's Bay, 

 the Ordnance Surveyors had measured each bed and marked all the 

 fossils that occurred in each ; when their lists were published it 

 would be seen that many species continued from the commencement 

 to the end of the Silurian series, because at that spot there was 

 no change of mineral condition. — Dr. Buckland wished to correct 

 a false impression not uncommon among novices, who hear only 

 debates and conflicts in disputable points in geology, that there is 

 nothing certain in the conclusions of that science ; and he wished it 



