1 64 The American Geologist. *^*"'>' ^^^s 
ceases, as shown by the obstruction at the mouth of the 
river itself, and the tendency of the marine currents is to 
fill the hollows. Here the reviewer would add a few words, 
as he has been anxious to discover the evidence of any 
other explanation for the phenomena of the submarine val- 
leys than that they were of atmospheric origin ; for one one 
knows better than Prof. Hull himself the startling conse- 
quences of such conclusions. As Dr. Gregory's "destruc- 
tive criticism" embraces the most comprehensive detail, 
they may be examined. When Dr. Gregory tells us that 
Prof. Hull's theory, which is an induction from ascertained 
phenomena, is based on an "improbable assumption"; that 
a channel carrving down mud may remain open, while a 
continental shelf of 7,000 feet or more in hight is being 
constructed, is a valid alternative theory; that the ''Hurd 
deep," with precipitous blufifs, lies in the line of warping, 
without offering evidence of fact ; that the Rhone canyon, 
in a small mountain lake is a parallel case to canyons in the 
continental shelf (and even the critic's assumption that 
such is not a true canyon is very much within the range of 
non-acceptance) that the Irish sea channel does not exist 
(Here Prof. Hull has not told the Whole story, but the re- 
viewer has verified the deepening channel from St. David's 
head to the edge of the continental shelf though possibly 
obstructed in the vicinity of 52-fathoms, it finally incises 
the slope to a depth of 6,810 feet, where its surface is sub- 
merged only 588 feet on one side and 3,000 feet on the 
other, and beyond to 8,400 feet) we are led to conclude that 
Dr. Gregory and others have found no satisfactory alterna- 
tive hypotheses, for lack of which is offered the above "de- 
structive criticism," but this utterly failing greatly strength- 
ens Prof. Hull's position. The clear analyses, though in- 
complete, of the valleys of the Adour and Congo are of the 
nature of monographs asked for. Even with these two 
absolutely complete, they could not have satisfied the 
hypothesis concerning the continental changes without the 
great amount of cumulative evidence which the author has 
assembled and skillfully woven into a chapter, the weak- 
ness of AVhich does not lie in such objections just men- 
tioned, but in not considering Dr. Gregory's position that 
