Terraces and River Valleys — Spencer. 157 
elevation of the land to a great degree caused the Glacial 
period. 
A sequel to this paper on submarine valleys adjacent 
to the British Isles is one continuing the investigations to 
the strait of Gibralter. 
It appears that Mr. Goodwin-Austin in 1849,* showed 
how the British platform is covered with shingle contain- 
ing littoral shells, sometimes unbroken, at depths of 80-100 
fathoms, as at Little Sole and Xymph banks, (Lat. 49° 
Long. 10° E.), and that the platform was terminated in a 
steep declivity. Goodwin-Austin concluded that these 
shell beds formed successive margins of the Atlantic before 
the present submergence. In 1853, Sir H. T. de la Bechet 
illustrated the late expanse of the land to the loo-fathom 
line, and observed that its width would not be much in- 
creased if extended to the 200-fathom line. He attributed 
the shelf to wave action and the distributing power of the 
tide. These early studied features have since been recog- 
nized by several writers, but none of them have indicated 
the real physical base of declivity, nor the river channels 
reaching down to it. Prof. Hull says that "The existence 
of such features * * * demands the admission of stu- 
pendous changes * * * as regards elevation and de- 
pression, such as naturalists might well hesitate to accept 
unless demonstrated by evidence of the most convincing 
kind. And. for myself. I fully admit that had it not been 
for the clear demonstration of several American geologists, 
but especially by that of Prof. Spencer, that the bed of the 
ocean along its western margin has been worn into terraces 
traversed by old river channels, down to depths of several 
thousand feet Ijelow the present level, it would probably 
not have occurred to me to ascertain whether these ph3^sical 
features characterize the bed of the ocean along its eastern 
margin." 
The continental platform ofif from France to Portugal 
is indicated on Dr. Stieler's Hand Atlas,? but there are no 
indications that it is trenched by river-like chan- 
* '-The Valleys of the English Channel" Q. J. G. S., vol. vi. (1849). 
t Geological Ofisener, 2nd Ed., np. fil-92. 
t Pub. by Justus Perthes, Gotha, 1872. 
