376 
GEOLOGY OF THE FIRST DISTRICT. 
Some of the strata thin out, and others take their places. Where derangements have 
occurred, it is frequently impossible to follow out all the original layers, in consequence of 
fracture, slipping and crushing of the strata. Some of these facts are illustrated on Plate 40, 
figs. 7, 8, 9, 10, and various figures on Plate 11. Fig. 10, of Plate 40, illustrates a fact of 
common occurrence where faults or slips are found, viz. the slate between the seams of fault 
is inclined at a high angle. 
Figures 2, 3, 4, 5, 6, 7, 14, of Plate 11, represent contortions in the rocks of this group 
along the Mohawk, between Cohoes falls and the Upper aqueduct, across the anticlinal axis.* 
Sections two to three miles west of Halfmoon landing.' 
No. 1. 
Feet. 
Slates. 
Compact grit. 
Slate. 3 
Slaty grit. 6 
Slate. 2 
Grit. li 
Slate. 14 
Grit. 1* 
No. 2. 
isiaie. 
Compact grit.. 3 
Slate. 5 
Grit. 1 
Slate. 4 
Grit. 8 
This section is one quar¬ 
ter of a mile west of No. 1.* 
No. 3. 
Feet. 
1 Compact grit. 5 
2 State. 12 
3 Compact grit... 6 
4 Slate. 0| 
5 Compact grit. 4 
6 Slate. 
This section is about one 
mile west of No. 2.* 
Section one and a half mile west of Rcxford flats. 
Section at an oblique favM one mile west of Rexford 
2 
3 
4 
5 
6 
7 
9 
10 
Grit ( greywacke). 
Slates . 
Grit... 
Slate . 
Compact grit, five layers.. 
Slates and shales. 
Grit. 
Slate.. 
Compact grit.... 
Slaty grit.. 
Similar alternations very numerous.* 
2 
5 
6 
7 
Slate. 
Compact grits 
Grit. 
Grit, compact, two layers. 
Grit, fissile... 
Slate and grits in very numerous layers 
and alternations.* 
Similar rocks, with similar alternations, are continually observed in the whole valley of the 
Hudson, within the limits designated as occupied by this group of rocks. The same axis as 
that described, extends through Saratoga lake. The rocks at Snake hill, a rocky peninsula 
on the eastern shore, and a bluff of rocks on the southwestern shore, show the effects of the 
upheaving action along this axis. Illustrations may be seen on Plate 11, figs. 8, 9, 10, 11, 
12, 13 ; and Plate 36, figs. 6, 7. 
Dr. Steel described these contortions in 1824.t He says, “The country around the lake 
is transition, and is included in the extensive tract of transition formation which extends along 
• These contortions were examined and sketched, and the sections made by Cadet Truman Seymour, one of the assistants, 
t Vide American Journal of Science, Vol. ix, p. 1, 4. 
