Mar., 1910.] 
Pennsylvanian Limestones. 
hi 
in the stream over a conspicuous overhanging ledge which extends 
from bank to bank. Xo better outcrop of the Lower Mercer is 
found anywhere than occurs here. At the fall the stratum lies 
in two layers in immediate contact and without any parting. 
The lower layer is 7 inches thick and the upper 2 feet, 5 inches. 
It is rather tough, blue-black, and quite fossiliferous. In the 
south bank in the roadway it lies at 1022 above sea, at the lowest 
point seen a few rods above the fall it lies 12 feet lower or a dip 
of 12 feet in a distance of about 150 yards. If the inclination 
observed in the cliff a short distance above the fall may be taken 
to indicate a continuation of the dip up to that point then this 
limestone in its trough probably lies 20 feet lower than at its 
crest near the bridge. 
On Turkeybroth, the north branch of Little Mill Creek, at a 
point 4 or 5 hundred yards above the fall this limestone again 
rises and becomes the floor of the Turkeybroth for some distance 
where it lies at about 1015. Near the top of the cliff a short dis- 
tance above the fall the Upper Mercer again outcrops and is 3 
feet, 1 inch thick. Its top lies 16 feet, S inches above stream. But 
it does not lie 10 feet above the level of the Lower Mercer’s crest 
at the bridge. The Upper Mercer is again quite well exposed for 
several hundred yards in the sides and bed of the south branch 
of Little Mill Creek. About 200 yards above the fork this stratum 
is seen in the south bank at 9 feet above stream, blue-black, very 
tough, and 3 feet, 2 inches thick with 10 inches of coal H feet 
beneath it. Up stream the limestone soon becomes the creek 
floor and is seen to undulate gently now above water and now' 
below' and gradually rising toward the east. For considerable 
distances where the stratum lies a little below water level and 
having been swept clean, there is seen to be a top layer 2 to 4 
inches thick, which is jointed so regularly as to look very like 
street paving. The jointing planes not being equal distances 
apart divide the layer into rectangular blocks 4 to 10 inches wide 
and 6 to 15 inches long. The jointing lines are very distinct and 
present a striking appearance in the still wrnter between the crests. 
It w ? ould seem that the blocks might be lifted easily but sq tightly 
do they fit that it is with difficulty that one is raised from be- 
tween its fellows. This pavement layer is more carbonaceous, 
nearly black, less tough, and much more fossiliferous than the 
thick layer beneath. 
At the point where this stream bends to the south the lime- 
stone disappears and is seen to dip sharply to the southward. It 
is not seen again for nearly a half mile, and then reappears rising 
above the stream bed at a point south of w'here it wrns last seen 
and lies 6 or 8 feet higher. This outcrop occurs about 200 yards 
below Mr. John Helsel’s barn. Both of these limestones wdiere 
exposed in the stream bed are seen to be jointed and lie in heavy 
