08 The American Geologist. February, its96 
Cuspate Fore lands. F. P. Gulliver, Cambridge, Mass. 
1 . Action of waves, tides and currents. Waves attack the whole coast. 
but erode more rapidly on headlands than at hay heads. Tides are less 
effective agents of transportation along shore on exposed coasts than 
currents, hut they are the important agents in sounds, channels and 
inlets. 
2. Current cusps, Type, Cape Hatteras. The cusp is formed in tin* 
dead water between two eddy currents. 
:s. Tidal cusps. Type, West Point, Puget sound. Washington. Cusp 
is formed between eddies 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 
Pugel 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 
yrate toward a region of uplift ami away from a region of depression. 
The relations of divides may therefore he significant indicators of up- 
heaval or depression, even when these are comparatively slight. Criteria 
were given by which these modifications may he 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, hut 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 historj . 
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 s\ s 
terns of Kentucky, and emphasized the value of the paper in helping to 
clear away points thai were previously obscure. 
Mr. Gilbkkt. in reply to a question concerning the effect of the rot a 
tion of the earth in modifying the courses of streams, estimated such 
elt'eet to he very slight and scarcely capable of detection, if it is at all 
present. 
Some fine Examples of Stream Robbing in the Catskill Mountains. 
N. If. Dartok, Washington. I). C. The Kaaterskill and Plaaterskill. 
two creeks flowing eastward into the Hudson river, have cut back 
