1892. | NEW YORK ACADEMY OF SCIENCES. (a 
although to ordinary observation the rocks seem harder. A ledge 
was found that could not have been more than 15 yards from the 
syenite, but the slide shows no appreciable mineralogical change. 
The sandstone is, however, rendered so crystalline at times, that 
it is difficult to detect its clastic character without a thin section. 
Connection between present topography and crystalline struc- 
ture.—Professor W. M. Davis has been giving much attention of 
late to the topographic development of this region,’ and the approxi- 
mate geological dates of many of the upheavals and drainage systems 
have been pointed out. The conclusions have a certain bearing on 
the age of thesyenite. The great dike exhibits over its outcrop a 
coarsely crystalline structure exceptin the case of the porphyry, which 
is probably a subordinate narrow intrusion. The orthoclase crystals 
even reach very large size, and the granitoid character of the rock 
indicates that it crystallized at a considerable depth, and was in no 
sense a surface flow. The outcrop stands now at the level of what 
Davis calls the Schooley peneplain, which marks the base-level of a 
post- -Triassic system of drainage. The dike must have suffered the 
erosion of this time, and perhaps of earlier cycles in order to expose, 
its coarsely crystalline portions, and it is reasonable to place its in- 
trusion at an earlier period. But as regards its age we are only 
able to say, that it is later than the Oneida conglomerate at the 
beginning of the Upper Silurian, and before the Triassic or late 
Triassic. During this long interval, there occurred the Carboniferous 
subsidence and post-Permian upheaval, and the dike may have been 
a concomitant occurrence with one of these. 
GeroLocicaL LABORATORY, CoLuMBIA COLLEGE. 
At the close of the paper many specimens illustrating the subject 
were exhibited, and the discussion was carried on by Pror. Brirron 
and others. 
The Secretary announced that the 50th Anniversary of the Hun- 
garian Society of Natural Sciences would be commemorated on 
January 17, 1892. 
Also that members of the Academy were invited to attend the 
meeting of the New York Section of the American Branch of the 
Society of Psychical Research to be held at Columbia College, 
February 10th, 1892. 
Meeting adjourned. 
1 W. M. Davis and J. W. Wood, Jr., Geographic Development of Northern 
New Jersey, Proc. Bost. Soc. Nat. Hist., vol. xxiv, 1889, 385, 411. W. M. 
Davis, The Geological Dates of Origin of certain Topographic Forms on the 
Atlantic Slope of the U. S., G. S. A., vol. ii, 559. 
