158 
HELDERBERG DIVISION. 
been made in the mass : in the instance exhibited in the annexed map, it is thirty rods 
wide, and the cliffs, though circular, run parallel with each other ; and the road space is 
as free of rocks, boulders, and fragments of cliffs, as any part of the adjacent country. In 
fact a clear sweep has been made directly into the rock to the depth of one hundred feet, 
and in width twenty-five or thirty rods, giving all this space for a forest, or, if necessary, 
for a meadow. Now it is imagined that these breaks or fractures in the rocks have laid 
the foundation for the numerous hillocks of the surrounding country, they being in a 
more advanced stage. They are composed beneath of insulated outliers of the same 
rocks ; but by the action of a variety of causes, the space between them and the main 
range of the same rocks is greatly enlarged. The accompanying map, which has been 
drawn by my friend George Geddes, of Tyler Post-office, will explain more than I am 
able by words, or by an elaborate description. M, M. Mounds ; L, L. Roadway, or, as 
it is called in the neighborhood by the significant name Splitrock. The map, for other 
details, explains itself. The roadway slopes east and west: the west part is perfectly dry ; 
on the south part, a small sulphur spring rises, which runs into a small pond b. The 
surface rock of the two hundred and fifty acres is the Onondaga limestone, and so it is 
on both sides of the roadway. It is difficult to account for such a separation, unless by 
subsidence of one side ; but as the rocks of the same kind correspond very nearly in height, 
an objection is thus interposed to this view ; though it must be admitted that this, after 
all, is the most plausible view, when taken in consideration with the nature of the rocks 
beneath, namely, the plaster beds and green shales, etc., which may in many ways be 
removed, and thus undermine the hard superior rocks. Whatever cause may have been 
instrumental in the production of this natural dry roadway, we certainly consider it as 
among the most interesting geological features in Onondaga county. They differ mate¬ 
rially from the deep ravines and gorges which constitute water courses (those, for instance, 
of the Genesee and Niagara rivers), in which, wherever they occur, if hard rocks form 
a part of the series, cascades or waterfalls are produced. On a magnificent scale we see 
this remark exemplified in the Niagara river, where the hard Niagara limestone forms a 
barrier in the form of a table, over which the waters pour, and send forth their everlasting 
thunders in their fall (See PI. X.). 
3. Impure gray porous limestone. 
I place this rock by itself under a distinct head, because it is an anomalous rock. It be¬ 
longs geologically to the preceding or second division of this series, the Onondaga-salt 
group. In position, it lies between the two plaster beds. The rock is extremely fine¬ 
grained, even, and compact between the irregular-shaped cavities. It is even-bedded, 
however, dividing distinctly into layers or strata, like other sedimentary rocks. The cavi¬ 
ties, or pores, as they exist in some places, are empty, certainly in all that part of the rock 
which is at or near the surface. It is sufficiently described, when it is said that it resem¬ 
bles very closely a lava. 
