Vol. 67.] ANNIVERSARY ADDRESS OF THE PRESIDENT. lxxxiii 



hand, movement may have been in comparative abeyance during 

 this part of the Cretaceous Period ; but this is so unlikely that I 

 am disposed to accept the second hypothesis. 



If that explanation be the true one, we must look upon the 

 Mesozoic as a period, not of rest, but of quiet epeirogenic movement 

 of a pulsatory character. The evidence obtained from the ' non- 

 sequences ' in the Jurassic rocks would seem to indicate that the 

 oolitic limestones were deposits of an exceptional nature in a sea 

 which was clear, shallow, and favourable for life, rather than deep ; 

 and that the clays of this System were formed in deeper water than 

 the alternating limestones. If this be the case, we are driven a stage 

 farther back to some more remote explanation of those alternations 

 which are so striking and tenacious a feature of the British strata 

 between the Inferior Oolite and the Portland Beds. By what 

 means was denudation so much quickened that even the deeper 

 waters of the period of marine advance became loaded with fine- 

 grained sediment over such wide areas ? Was it merely the 

 exposure at certain periods of material that was more easily 

 denuded into fine mud ; or is it not more likely that the climate 

 may have varied periodically, and that denuding forces Avere corre- 

 spondingly quickened and retarded? 



(d) Recurrence of Type in Cycles of Deposition. 



Marcel Bertrand, in a most suggestive and illuminating memoir, 

 endeavoured to correlate the successive types of deposit preceding and 

 following the movement periods of different dates with one another. 

 In this he obtained considerable success, but in some instances, it 

 seems to me, he rather strained the facts to bring them into con- 

 formity with his ideas of recurrence. Such recurrence is certainly 

 traceable throughout the British record, but it is generally overlaid 

 with differences so striking that the interference of other causes 

 with a different periodicity must be suspected. This statement will 

 become clearer when we examine a few examples and exceptions. 



The remarkable resemblance of the sandy sediments of the 

 Torridonian, the Old lied Sandstone, and the New lied Sandstone 

 is a commonplace in British descriptive geology. 



The Torridonian and Old Red Sandstone breccias, probably 

 associated with maximum uplift, may be correlated with the 

 Brockrams and the other Permian breccias. 



The well-rounded pebble-beds of the Bunter constitute a type 

 which we see anticipated in both Torridonian and Old Red Sand- 

 stone conglomerates, and followed to a certain extent by those of 



