389 
[Davis and Wood* 
level and of shore line during Cretaceous time, but the changes do 
not appear to affect the present topography of the country. During 
all this time, the more resistant crystalline rocks were worn lower 
and lower, and so the almost completion of the old Schooley base- 
level plain in Cretaceous time followed the good beginning made in 
Jurassic time. 
Since first reaching the above conclusion, McGee’s articles al- 
ready referred to 1 have given us information of an oscillation of 
level that took place after the early wearing down of the Highlands 
had been well advanced. It was in the sense of an elevation dur- 
ing which narrow valleys of moderate depth, from one to two 
hundred feet, were cut to be filled again when depression allowed 
the accumulation of the lowest member of the superposed series, 
the Potomac formation of this author. Another elevation is re- 
corded by the unconformity between these first deposits and the 
superposed members of the Cretaceous series. This was followed 
by a second depression. These facts were discovered by obser- 
vation on the ground and are of manifest geologic importance ; but 
they do not appear to be recorded in the present topography of 
the country, and were not discovered in our study of the maps. If 
of more recent date, they would be visibly recorded in the form 
of the surface ; and it will be seen that as we take up the later chap- 
ters of the history of New Jersey, brief subdivisions of time mark- 
ing slight oscillations of level attain importance. Similar subdivi- 
sions of ancient time would be called for by a full knowledge of 
past history ; and the Schooley C3^cle must be regarded as containing 
many sub-cycles, not traceable in our method of study. In the gen- 
eral sequence of geographic development, our conclusions agree 
substantially with those reached by McGee. 
20. General drainage system in the Schooley cycle. The introduc- 
tion to our essay has explained what is meant by a geographic cycle. 
We must now consider the conditions of drainage during the cycle 
of development when the land stood at the Schooley baselevel, and 
the sub-cycle at the end of this division of time, when the land was 
somewhat depressed, allowing the transgression of the Cretaceous 
ocean. It does not appear practicable at present to inquire closely 
into the early stages of Highland drainage, for this would carry us 
into questions of geological structure on which there is not yet 
reached any general agreement. Our own feeling is that the early 
J Amer. Journ. Sci., XXXV, 1888, 134, 135, 141. 
