NORTHERN END OF THE HELDERBERG PLATEAU 71 



10 Crinoid stems 



The total thickness of the formation, is not shown in these 

 quarries. The Tentaculite capped by the lower part of the Penta- 

 merus limestone, as seen in the eastern quarry, is very well shown 

 in the accompanying picture. The Tentaculite and Pentamerus 

 limestones are quarried and burned for quicklime, and they are 

 also used in the manufacture of the artificial or portland cement 

 now made by the Helderberg cement co. at this place. An 

 analysis of the Tentaculite limestone reported by Mr Schaeffer 

 is as follows: 



Silica 1.48 



Carbonate of lime 95.75 



Another of the Pentamerus limestone gave the following result: 

 Silica 4.12 



Carbonate of lime 93 . 68 



Mr Schaeffer reported the dip as 23 inches to 100 feet about 

 sw along the railroad track and 21 inches to 100 feet more 

 nearly south in the tunnel. S. Norton, manager for the Helder- 

 berg cement co., gave the dip as 20 inches to 100 feet sw. 



To the south of Howe's cave and Cobleskill creek is a steep hill, 

 rising about 1000 feet above the level of the creek. This hill 

 affords a fair section of the formations in this region, and the 

 following gives their approximate thickness. 



Feet 



8 B 1 Covered from the level of the Cobleskill to the 66=66 



base of the lowest massive limestone, which is 

 apparently about at the junction of the Tentacu- 

 lite and Pentamerus. 



B 2 Massive Pentamerus limestone, the lower ledge 53-119 

 22f feet thick; then a covered slope with a 

 shattered ledge at the top. 



B 3 Shaly limestone; mostly covered slope with only 95=214 

 a little of the limestone shown at the top of the 

 formation. 



B 4 Becraft; massive, light gray limestone, forming 15=229 

 a steep ledge from 15 to possibly 18 feet in thick- 

 ness. 



