304 Scientific Intelligence. 
of the country. 
he mec is still unfinished in the western part of the State; 
but w esau indications of what we may expect to say on farther 
sR a n.— Proc. Amer. Assoc., Detroit, 1875, p. 8 
ihe Erosion of Rocks ; b - E. B. ANDREWS. (Commas 
si to the Editors, dated Lancaster, Ohio, Sept., 1876.)— 
Attention having been ‘vecently called to the subject of erosion 
by the excellent papers of Mr. G. K. Gilbert, I beg a_little space 
" oh sige one feature of the weathering of rocks, which may 
orthy of more consideration than it has receive 
wen is likely, at least for some time, to remain undetermined in 
ome parts 
valleys bordered by high cliffs, from fifty to two hundred feet 
high. These cliffs often overhang their bases forming recesses 
from thirty to one hundred and fifty feet in depth from a vertical 
line dropped from the top. These rock-walled valleys when fol- 
lowed up are often found to terminate in semi-circular cliffs over 
which the little streams fall in pretty cascades. Behind the falls 
of mud se the walls of the cavern. us spray beco svn bis 
agent of undermining the cliff, just as the <a pov 
‘ bearing-in” in the lower art of the coal In 
projecting alpsnee fall and the pie: is practically fo — 
is Way an enormous amount of valley erosion na valley yenalig 
ear the “ 
Cave is itself only a remnan token spray-cav was 
cliff formed a dry and aes shelter, ie ithe rece reoess 
* The erosion at the Falls of Niagara, by spray driven by wind oe 
is referred to by Lyell, in his account of the region given Ne York —_ 
in North America,” page 26, and also by Prof. James ss ememinainstetet 
logical Report. 
