Vol. 67. j ANNIVERSARY ADDRESS OF THE PRESIDENT. 1\V 



much farther in the interpretation of the physiography of the past. 

 Put our guide must be the union of delicate stratigraphical research 

 with minute geographical work. We must be accurate in our 

 geological facts ; but we may, as Darwin advised us, speculate 

 freely, and our lode -star should be the injunction to 'travel. 

 travel, travel.' 



(2) The Cycle of Earth-Movement. 



The geological record of a single region such as Britain is a 

 chronicle of two chief classes of events. On the one hand, the 

 great masses of sediment record periods of downward movement, 

 more or less interrupted, during which the area was covered by the 

 sea or other widely extended waters ; while, on the other, the 

 physical breaks in sedimentation, and particularly the great un- 

 conformities, furnish us with evidence of uplift into the regions 

 of denudation, mostly areas of land or relatively shallow water. 



The study of the British record tells of many pulsations of 

 movement, varying in direction and intensity, but each one 

 accompanied, on the whole, by cycles of phenomena, similar in their 

 march of events, but varied in other details by the external conditions 

 under which they were developed. 



(3) The Cycle of Deposition. 



The general succession is approximately as follows : — 



(i) A deeper-water or ' thalassic ' period, with widespread, even- 

 bedded, fine-grained, seaward, sediments, succeeding or alternating 

 with organic deposits. 



(ii) A shallower-water period, with ' deltaic ' and littoral, shore- 

 ward, deposits of mudstones and sandstones more limited in their 

 distribution, but laid down on smooth areas, associated with 

 phenomena of contemporaneous erosion and overlap, with increasing 

 coarseness of grain and with decreasing numbers of organic 

 remains. 



(iii) A period of rising and uplift giving origin to continents, 

 mountains, and lakes, to rapid denudation filling the hollows thus 

 formed with irregular masses of coarse-grained, 'terrestrial,' land- 

 ward, deposits which are variable in their composition and source, 

 difficult to correlate, characteristically poor in organisms, and 

 frequently associated with sheets or masses of locally derived 

 and angular or slightly rounded materials. 



(iv) A period of sinking and depression, during which the sea 



