154 The American Geologist. March, i905 
reached 6000 feet. The edge of the submerged terrace 
(continental shelf), supporting the British Isles, is gener- 
ally known as the lOO-fathom line, but this is misleading 
as the features vary and "only by a close observance of 
the change of depth, as indicated by the soundings"' can 
the features be recognized. In front of the platform the 
grand escarpment or continental slope, off Britain, descends 
steeply 7000-8000 feet, in some cases precipitously. Off 
Scotland the margin of the shelf is near the loo-fathorn 
line, but in front of the English channel, it is at a depth 
of 180-200 fathoms. At some points the shelf is reduced 
to a breadth beyond the islands of 50-70 miles, while off 
Porcupine bank it extends for 180 sea miles beyond the 
coast of Ireland, and forms a peculiar peninsula, eft'ectively 
sho\yn on his map, enclosing an embayment receiving the 
Shannon channel at its head. It is shown to extend to a 
depth of over 9000 feet. From his work on the submarine 
topography, it would be appropriate to name it the Hull 
embayment, especially as he has done much more to eluci- 
date the phenomena than any one preceding him, and he is 
an Irishman, too. Also the still more remarkable embay- 
ment, of similar depth, is shown between Ireland and Rock- 
all attaining a breadth of 125 miles. It heads in an am- 
phitheatre or great cove in the Scotland-Faeroe ridge, 
where this submarine feature is crossed by the Lightning 
channel, which is the drowned col between this and an- 
other deep channel extending down the slope to the basin 
of the Norwegian sea. 
The continental shelf is almost level, having been cov- 
ered with water-borne sediments or earlier glacial deposits. 
The formation of the continental shelf by marine action on 
emergent lands of such plateaus as the British platform 
has been described by Prof. James Geikie* who also 
noticed "the abrupt descent from the edge of the plateau," 
but he does not appear to have recognized that such feat- 
ures must have had a terrestrial origin, as the surface is 
sculptured with river channels. 
From the west of Ireland Hull traces the courses of 
t T-rans. Vict. Inst. Vol. XXIV, p . 205. 
* Ptoc. Roy. Geog. Soc , 1892, p. 639, p. 644. 
