104 The American Geologist. Aug^t, iqob 
They are very porous and light and have the smooth joint 
surfaces of chert. The top of the hill west of Grand Sum- 
mit registered 90 feet above the town. Taking the dip into 
consideration this would add more than 90 feet to the 
Grand Summit section. The dip to the west is probably 
equal to the railroad grade. 
The limestone quarried at Cambridge may be number 
25 of our Grand Summit section, but it seems probable that 
it is one a little higher in the series. At Grand Summit 
there are four layers of limestone with intervening shale 
beds of considerable thickness, between the top of our sec- 
tion and the base of the Wreford limestone. The lime- 
stone quarried west of town at Cambridge is 94 feet below 
the base of the Wreford limestone. The latter is excellent- 
ly exposed across the creek south of the quarry, where a 
fairly good section of the underlying rocks is to be had, on 
the point just east of the mouth of the little tributary from 
the south. The following section is a compilation of this 
exposure with those from the old Torrence station, just west 
of Cambridge, along the railroad to Burden. From Tor- 
rence (old station at the Creek) to Burden at the top of the 
escarpment almost all the strata are excellently exposed. 
THE SECTION FROM CAMBRIDGE TO BURDEN. 
39. Chert concretions and weathered limestone, 
top of Burden cut 2+ ft. inches 
38. Limestone, massive, with chert in layers 10 " " 
37. Limestone with numerous chert concretions .. 10 " " 
36. Shaly calcareous layer with some fossils 3 " 6 " 
35. Limestone, shaly, full of pelecypods 2 "0 " 
34. Shales, dark red and blue 6 " 6 " 
33. Shales, bluish 3 " " 
32. Bluish marl 1 " 
31. Shale, red 4 " " 
30. Limestone, shaly below 2 " " 
29. Covered 20 " 
28. Shale, bluish, and calcareous nodules "6 " 
27. Massive limestone, two layers 5 " 6 " 
26. Limestone, impure, shaly; shales on top .. '2 " " 
25. Shales, blue and olive . . . ., 9 " " 
