98 
The American Geologist. 
February, 1896 
Cuspate Fore-la rich. F. P. Gulltvek, Cambridge, Mass. 
1. Action of waves, tides and currents. Waves attack the whole coast, 
but erode more rapidly on headlands than at bay heads. Tides are less 
effective agents of transportation along shore on exposed coasts than 
currents, but they are the important agents in sounds, channels and 
inlets. 
2. Current cusps. Type, Cape Hatteras. The cusp is formed in the 
dead water between two eddy currents. 
3. Tidal cusps. Type, West Point, Puget sound, Washington. Cusp 
is formed between e*ddies of in- and out-flowing tides. 
4. Delta cusps. Type, Tiber delta, Italy. The mouth of the river 
forms the point of the cusp, on either side of which the alongshore cur¬ 
rents arrange the detritus. 
In discussion, Mr. Bailey Willis spoke of other examples in the 
Puget sound region. 
Drainage Modifications and their Interpretation. M. R. Campbell, 
Washington, D. C. The paper opened with a discussion of the sub¬ 
ject of stream modification under the influence of slow elevation or de¬ 
pression of the earth’s surface. From this is derived the law of the 
Migration of Divides which controls, to a greater or less extent, the 
alignment of all drainage systems. According to this law, divides mi¬ 
grate toward a region of uplift and away from a region of depression. 
The relations of divides may therefore be significant indicators of up¬ 
heaval or depression, even when these are comparatively slight. Criteria 
were given by which these modifications may be recognized and the 
character of the crustal movement determined. 
Next followed a brief description of some of the drainage systems of 
the Appalachian province, south of the glaciated region, to show that 
similar modifications of the drainage are of common occurrence, not 
only in the regions of horizontal rocks, but also in the highly complica¬ 
ted geologic structure of the Appalachian valley. It was shown that 
some of these changes are recent, whereas some probably date back to 
the time of the Jura-Trias depression. 
The principal object of this paper was to show that the drainage of 
the Appalachians constitutes a record of Mesozoic and Cenozoic history, 
and that this record is to the physiographer of equal importance to that 
contained in the forms sculptured from the surface of the land. 
Prof. Shaler, in discussion, noted the relations of the drainage sys¬ 
tems of Kentucky, and emphasized the value of the paper in helping to 
clear away points that were previously obscure. 
Mr. Gilbert, in reply to a question concerning the effect of the rota¬ 
tion of the earth in modifying the courses of streams, estimated such 
effect to be very slight and scarcely capable of detection, if it is at all 
present. 
Some fine Examples of Stream Bobbing in the Cat skill Mountains. 
N. H. Darton, Washington, D. C. The Kaaterskill and Plaaterskill, 
two creeks flowing eastward into the Hudson river, have cut back 
