Terraces and River Valleys — Spencer. 1 53 
would make a large brochure. From these, we learn of a 
vast number of valleys -and systems of valleys indenting 
the continental shelf and forming submarine topographic 
features resembling those produced by atmospheric agents, 
such as are found on the American side of the Atlantic and 
in the \\'est Indies. The shelf has been more or less 
studied since the time of Mr. Goodwin-Austin (i849).t 
But Prof. Hull's valleys throw new light upon their forms 
and sculpture, and indeed upon the whole question of great 
changes of level of land and sea. He further applies these 
changes to one of the many consequences thereof, namely 
the possible cause of the glacial period. As Prof. Hull's 
papers are not easily accessible to many on this side of the 
Atlantic, a review of the leading features appearing in one 
of our journals will extend the knowledge of what has 
been done in a subject embracing one of the most wide- 
spread groups of physiographic phenomena, which how- 
ever has attracted little attention in this country, except 
that of two or three of us, although these have sown seed 
which is bringing forth a rich harvest in the old world. 
The British platform extends to Iceland and Green- 
land, as shown by previous investigators. "This former 
connection is placed beyond doubt by the character of the 
fauna and flora."* Dr. Alfred ^^'allace includes Ice- 
land with Europe in his Palaearctic region. Prof. Xew- 
ton has shown that all the mammals of Iceland, except 
three Arctic forms, are European. Dr. AX'alker's studies of 
the botany and entomology- of Iceland also witnesses the 
late connection with the British islands. In Greenland 
some forms are European, others are American and still 
some are Arctic. If a biological survey suggests the ex- 
tension of European life beyond the present continent, 
which implies an elevation of the land, then 5uch should be 
indicated in the submarine topographic features now sub- 
merged, and these are Prof. Hull's studies. He says that 
the charts show that an elevation of 1320 feet (except in 
the relatively narrow trench 2000 feet deeper) would con- 
nect Iceland with Europe, but the actual altitude may have 
t Q. J. G. S., vol. xxii, p. 240. 
* From the chapter relating to the British olatform. 
