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



Whatever irregularities there may have been in the accumulation 

 of the shallow-water deposits of the preceding phase, they will be 

 intensified in the terrestrial deposits which are laid down in this 

 succeeding phase of uplift, and they will be correspondingly difficult 

 to correlate and arrange in order of time. Screes and gravels — 

 the result of frost and torrent action, and even sands formed in the 

 air, must necessarily be pushed outwards from their sites of origin ; 

 and if, during this outward migration, sheets of such materials 

 originate, it is clear that the different parts of any one of them 

 must be of different dates. 



To a smaller extent the same is true of lacustrine deposits, and 

 there must be an outward progression from the shores towards the 

 deeper parts of these water-holding basins. 



The materials deposited during the phase of uplift show a 

 tendency towards one of two extremes ; they are characterised either 

 by their angularity, or by the great amount of corrasion which they 

 have undergone. Debris broken up in the air, whether accumu- 

 lating in air or water, whether carried directly by gravitation, by 

 land -slips, or by ice, tends to retain its sharply broken edges. But 

 water-transported matter carried by high- velocity streams becomes 

 exceptionally well-rounded, and material fine enough to be carried 

 by wind becomes smoothed and polished. 



Prof. Charles Lapworth has drawn attention to the fact that one 

 of the physiographical results of orogenic movement, accompanied 

 by denudation, is the tendency to intensify the production of longi- 

 tudinal valleys. There is observable in the Alps, and probably 

 elsewhere, a similar connexion between earth-movement and the 

 formation of breccias. Excessive formation of screes and landslips 

 is found to be associated with the outcrop of thrust-planes. In the 

 quickened denudation brought about by the steep slopes thus 

 maintained there may possibly be found one explanation of the 

 frequent association of breccias with mountain-building. 



Torrent-formed gravels are shot down immediately at the foot of 

 mountain-land, whether this abuts on sheets of water or on areas 

 of flat sediment recently formed or newly lifted. The first-formed 

 mass of gravel alters the conditions of slope and [velocity, and 

 successive loads are carried farther and farther outwards until 

 they reach gentler slopes or stiller water, and are perforce deposited 

 there. Thus the mass grows outwards from the area of denudation, 

 each increment being laid down against the preceding one on the 

 surfaces that we know as planes of ' false bedding/ These planes 

 are, therefore, the true ' time-planes ' of contemporaneous deposit 



