286 PROF. E. HULL, LL.D., ETC., ON THE SUB-OCEANIC 



It now only remains for me to endeavour to explain the 

 process by which, as we may conjecture, the physical features 

 under the waters of the x\tlantic were developed. 



II. Mode of Formation of the Sub-Oceanic Features. — 

 It need scarcely be observed that there is extreme difficulty 

 in the endeavour to sketch out the modus operandi accord- 

 ing to Avhich the physical features here described were pro- 

 duced. To begin with, we are ignorant, to a great extent, 

 of the form and coiiditious of the oceanic bed at the com- 

 meneement of the Tertiary period. During the Cretaceous 

 period there was Avide prevalence of oceanic conditions and 

 great depression of the land. With the introduction of the 

 Tertiary period, elevation of the land commenced, becoming 

 accentuated throughout the Mio-Pliocene periods, and pro- 

 bably attaining its maximum result at the commencement of 

 the Pleistocene or Glacial epoch.* The initial effect of the 

 emergence on a surface gradually sloping down from the 

 enjergent lands to the abyssal regions of the ocean, would 

 be the formation of " a plane of marine denudation," to use 

 the phrase of the late Sir AndreAV Kamsay. This gradu^illy 

 sloping plane, levelled and eroded by wave-action during 

 the prucess of emergence, is now represented by, though not 

 conterminous with, the British and Continental Platform. 

 Ultimately, when the elevation of the sea-bed a.ttanied its 

 maximum, and a prolonged pause occurred, wave-action 

 came into full play, cutting back the emergent lands along 

 "the base-level of erosion," a process continued during 

 subsequent subsidence and submergence down to the present 

 day. 



Aleanwhile the rivers draining the land areas, both present 

 and past, were at work in wearing down their channels 

 through the Continental Platform ; channels which, as we 

 have seen, are still traceable by aid of the soundings down 

 to the very base of the Grand Declivity. I regard the 

 long lapse of the earliest glacial period, that of intensest 

 cold and of severest glacial conditions, as that during which 

 both wave-action along the base of the D(^chvity, and river- 

 erosion over the Platform, were most effective. It was only a 



* The researches of the Swiss and German geologists Heiui, Baltzer, 

 Schardt, Eenevier and others, show tliat in the Alps and .Jura the most 

 stupendous terrestrial movements occ-urred after the close of the Miocene 

 period, that is during the Pliocene ; as Miocene bed.«, both lacustrine and 

 marine, have beeir tlexured, folded, and U2jlifted several thousaird feet 

 amongst these regions. 



