of the Catskill Mountains. 447 
geological questions raised by the topographical features, indi- 
cated in this paper, requires a careful and exhaustive strati- 
graphical study which it was impossible for me to undertake ' 
while the arduous topographical and hypsometrical work de- 
manded all my time and attention. This must remain for 
future investigation. Meanwhile, however, I will add here a 
few preliminary suggestions. 
The masses of rocks forming the Catskill Mountains were 
deposited in a gulf of the Devonian Sea comprised between 
the Adirondack plateau and the Green Mountain range, includ- 
ing the low Silurian ridges between the Hudson and the foot 
of the Catskills, all of which were probably emerged when the 
Devonian age began. Most of New England was also above 
the level of the ocean. The thickness of the sediments shows 
that the bottom of this gulf gradually subsided during that 
time to a depth of some 5000 feet, constantly making room 
for new deposits. 
The presence of the gray conglomerate capping the highest 
hills proves that the deposition of these sediments continued 
into the Subcarboniferous period, after which they were 
upheaved above the level of the ocean, before the deposit of 
the Coal-measures, and have remained emerged ever since. 
The slight southward dip indicates that during the Devon- 
ian age a general aud gradual rise of the continent took place 
from the north, which raised successively above water parts of 
the Lower and Upper Silurian, in the, Helderberg and Oris- 
kany sandstone, which were laid dry when the Catskill sand- 
stones and shales were still depositing. 
The most notable upheaval of the Catskill region probably 
took place at the time of the great revolution which raised the 
main Appalachian system ; doubled the size of the early con- 
tinent and closed the Carboniferous age. But the peculiar 
situation which sheltered it from the immediate effect of the 
form of that portion of the western Behe 
A glance at the sketch (Plate XIX) will show that, when this 
