1893.] Geology and Paleontology. 1083 
would pile up behind it and presently sweep it on. Looking up the 
nala we could see the sides of it constantly falling in and their ruins 
` carried down. Three times did the nala yield a frightful offspring of 
this kind, and each time it found a new exit into the main river below, 
and entirely changed the shape of the fan. The third avalanche was 
the largest of all, and fortunately left a causeway of stones, reaching 
almost across the nala, at our very feet. Some big fall must have pres- 
ently taken place higher up and dammed back the waters, for the stream 
ran almost dry and we were enabled to cross the gully without 
difficulty. 
“ Assuming that one of the avalanches we saw travelled at the rate 
of only 7 miles an hour—200 yards a minute, and took only 7 
minutes to pass any point, it would be 1400 yards long. Call its 
average width 8 yards, and average depth 2 yards, it would consist of 
over 10000 cubic yards of stuff. Suppose three-fourths of this to have 
been water, you get 2500 cubic yards of débris discharged by one of 
these avalanches, and we saw three come down a single gully, where 
others had fallen before we arrived and others fell after we left. 15000 
cubic yards is a low estimate for the fall of that one day down that 
single and relatively small gully. One gully of this sort to every mile 
of valley isa minimum computation. It is easy to see then what a 
powerful element mud avalanches must be in determining the physical 
. features of this region of the earth.” (Geog. Journ., Oct., 1893.) 
Cladodont Sharks of the Cleveland Shale.—The fossil sharks 
recently discovered in the Cleveland shale are of especial interest 
and importance because they show definitely the form of structure 
of these early Elasmobranchs. Professor E. W. Claypole has made 
them the subject of a paper in the American Geologist, May, 1893. 
The material now at hand represents four species of Cladodus, and two 
of Monocladodus. These genera are closely allied, but the absence of 
- lateral denticles, in the opinion of the author, marks a generic differ- 
. M. clarkii is distinguished by the fact that the teeth stand in 
pairs, one close behind the other. M. pinnatus is represented by asingle 
specimen which is unique from the great strength of the ventral fins, 
whence comes its specific name. Both of these species are figured, 
together with Cladodus sinuatus, C. clarkii, and C. rivi-petrosi. Pro- 
fessor Claypole gives also an amended description of Newberry's C. 
repleri. The genus Monocladodus is very near to, if not identical with 
Styptobasis Cope. * 
