GEOLOGICAL SKETCH. 5 
These quarries have furnished much of the building material employed in 
our cities, and the fronts of fully one-half of the residences of New York 
are composed of ‘ brownstone,” as it is called, derived from them. 
The thickness of the Triassic series in the Connecticut and Palisade 
areas is 5,000 feet or more, and the arrangement of the strata among them- 
selves is peculiar and as yet not satisfactorily explained. In the Connecticut 
area the rocks all dip toward the east, the outcropping edges of the trap 
sheets left in strong relief by the erosion of the associated beds forming the 
bold escarpments of Hast Rock and West Rock, at New Haven, Conn., 
Mount Tom and Mount Holyoke, in Massachusetts. In New Jersey, on 
the contrary, the dip of the Triassic beds is generally towards the west at 
an angle of from three to fifteen degrees with the horizon, and the edges of 
the trap sheets form bold cliffs, which face the east and constitute the sum- 
mit of the ridges known as the Palisades, First and Second Newark Mount- 
ains, etc. In addition to these sheets of trap the strata are cut by many 
dikes of diabase, which cross them vertically or at a high angle. 
The origin of the singular structure I have described has been much 
discussed. Many of the beds show ripple-marks, sun cracks, and rain-drop 
impressions, which prove that they were once beaches or mud flats, some- 
times exposed to the air. They are also frequently impressed by the tracks 
of large and small animals, generally three-toed, but sometimes showing 
four or five digits. These were at first supposed to be for the most part 
the tracks of birds, but are now believed to have been made by reptiles and 
amphibians. We have here autographs of perhaps one hundred different 
kinds of animals of which scarce any other record has been discovered, a 
few scattered bones and one or two imperfect skeletons being all yet found 
of the creatures themselves. Everything indicates that these tracks were 
made by animals that frequented the shores of bays and estuaries where 
the retveating tide left broad surfaces which were their feeding grounds. 
Inasmuch as many successive beds show ripple-marks, sun cracks, and tracks, 
the conclusion seems inevitable that the areas where these strata were de- 
posited were slowly sinking and that the land-wash spread by the tide 
constantly formed new sheets, upon which fresh records were inscribed. 
The downward movement must have been very slow, for it apparently about 
