136 TRANSACTIONS OF THE [JUNE 6, 
treal, from localities in central and southern central New York, 
which are recognized as Hamilton and Chemung or Middle Devo- 
nian. That these rocks resemble, lithologically, some of the flag- 
ging-stones of the Hamilton in Ulster, Sullivan, and Greene counties 
is evident at once on a cursory examination. The absence of any 
remains of animal life leaves the full proof of geological equivalency 
in doubt. The great thickness of conglomerate at the top, and the 
prevalence of gray and green shales, with the red shales and sand- 
stones, look more like the Catskill rocks or Upper Devonian. It is 
safe, however, to put them in the Middle Devonian.’' Professor 
Smock also measured the thickness of the Devonian rocks of Skun- 
nemunk Mountain, and considered them from 1300’ to 1600’ in 
thickness. It was stated that ‘‘In the east and west slopes of 
Skunnemunk mountain, New York, the strata are beautifully laid 
bare in the beds of small streams, and, as the dips are at small 
angles, the height of the crest above the valleys on each side ap- 
proximates to the thickness of strata in these sections. The highest 
crest has a maximum elevation of 1600 feet above tide level; the 
valley on the west is about 600 feet; that on the east 300 feet, 
making a difference of 1300 feet for the height of the mountain. 
A still better exposure of these rocks is seen on the road west, 
descending the mountain from the Seven Springs Mountain House. 
This section, three-quarters of a mile long, shows a nearly unbroken 
succession of ledges, whose beds have a nearly uniform dip of 20° 
toward the east-northeast. Allowing for the difference in the 
length, as measured on the line of the dip, and taking 20° as the 
mean descent of the strata, the thickness, as computed for these 
elements, would be at least 1300 feet. If to this figure be added 
300 feet for the conglomerate, which is not in the section, there is 
a total of 1600 feet.’” 
This report was reviewed by Mr. N. H. Darton,’ who has added 
somewhat to Professor Smock’s historical account of the formation, 
and who has spent a considerable amount of time in studying the 
structural relations and mapping this series of rocks. The discovery 
of fossil plants and their evidence as to the geologic age of the 
formation were mentioned by Dr. Hunt in 1886.* 
In 1886 Professor F. J. H. Merrill studied this series of rocks in 
New Jersey; and in the blue limestone below the Devonian sand- 
stones and shales he was fortunate enough to find a few species of 
Lower Helderberg fossils, as Spirifera Vanuxemt, Chetetes Hel- 
derberguz, ete.; while in.an overlying calcareous conglomerate and 
siliceous grit are Oriskany and Upper Helderberg (Corniferous) 
fossils.° 
1 Op. cit., pp. 54, 55. 
2 "Op. cit., p. 06: 
8 Scientific American Supplement, vol. xix, June 13, 1885, pp. 7877, 7878. 
4 Mineral Physiology and Physiography, p. 591. 
5 See Geol. Surv. New Jersey, Ann. Rept. State Geologist for 1886 (1887), 
pp. 113, 114. 
