REVIEWS AND BOOK NOTICES. 735 
by the torrent. The aggregate of the forces which have continued 
in operation through a series of ages, which no man can determine 
now, and which we agree to denominate meteoric or atmospheric, 
are the combined action of water, air and ice. These forces have 
undoubtedly been far more effective in ages past than at present.” 
One of the latest geological occurrences in this region, as well 
as over the world generally, is the formation of the terraces occa- 
sionally found bordering rivers. In a basin of the Madison River 
is a remarkable system of terraces represented by Fig. 179. 
While usually in the terraces of our eastern rivers, and in fact 
rivers generally, those on opposite sides are of unequal height, 
here each terrace is uniformly of the same height as the one 
opposite. 
In Montana neither are the anticlinal folds or synclinal valleys 
so distinctly defined as in the interior basin of Utah, but the prom- 
inent features are the widely extended areas of elevation. 
Geologists will be interested in a feature of the geological struct- 
ure of the mountains of Montana, ‘‘ observed by the survey of the 
past season for the first time and not noticed in such a marked de- 
gree in any other portions of the west.” This is the inversion of 
the sedimentary beds, so that the oldest incline at a greater or 
less angle on those of more modernages. The mode of formation 
of canons and river valleys is reserved for future discussion, but 
attention is drawn to the ‘‘ fact that the streams seem to have cut 
their way directly through mountain ranges, instead of following 
synclinal depressions.” This, he says, indicates that they began 
the process of erosion at the time of the commencement of the 
elevation of the surface. ‘*This is shown all along the valley of 
the Yellowstone and more conspicuously in the valleys of the 
Madison and Gallatin which have carved immense caiions or 
gorges ee through two of the loftiest ranges of mountains in 
Montana. 
The action of glaciers in causing this erosion Prof. Hayden 
thinks to have been local, and he regards the superficial or drift 
deposits, which sometimes are very thick, as of local origin. “As 
I have so often stated in my previous reports, I have never been 
able to find any evidence in the wees | Mountain region of what is 
usually termed a northern drift.’ 
It will be seen how much geographers and geologists as well as 
lovers of the marvellous and beautiful in nature are indebted to 
