Mar., 1910.] Pennsylvanian Limestones. m 



in the stream over a conspicuous overhanging ledge which extends 

 from bank to bank. No 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, o 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, 8 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 Ih 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 -l 

 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 water between the crests. 

 It would seem that the blocks might be lifted easily but so 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 fossiliferovis 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 where it was 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 where 

 exposed in the stream bed are seen to be jointed and lie in heavy 



