EXTENT OF FOLDING AND SUBSEQUENT EROSION 463 



Eastward at Lockport and Medina certain of the upper beds are quite 

 fossiliferous, sometimes presenting almost the character of an organic 

 rock. Such agglomerations consist of the shells of Pleurotomaria parve- 

 tusta, Buccania triloba, Isochilina cylindrica, and Pelecypods, especially 

 the two "Modiolopsis" before mentioned. Lingula cuneata is also com- 

 mon, especially on slabs of higher sandstone, where single valves often 

 show the arrangement adopted by modern bodies on a flat beach under 

 the influence of the run-off of the waves. Wave-marks are also associated 

 with these fossils, the ensemble being clearly one of beach phenomena. 

 Still farther east, at Eochester, the series becomes almost unfossiliferous. 

 The line of contact between the Medina and Queenston is here obscure 

 and marked by the appearance of coarser sediments. Some of the upper 

 beds are even pebbly and most of the series is sandy. Several heavy 

 sandstone beds occur, and these usually show marked cross-bedding com- 

 monly of the eolian type, but some torrential bedding also occurs. These 

 latter beds near the top also show ripple-marks. Fossils occur just below 

 the Thorold quartzite and are chiefly Arthrophycus harlani, Daedalus, 

 and other structures of this type. Sarle 68 has interpreted these as the 

 work of burrowing worms, an interpretation which may hold for the 

 Daedalus, but scarcely for the Arthrophycus. The latter always projects 

 downward from the under side of sandstone into the mud layers beneath, 

 and thus represents the natural mold of a series of grooves, with charac- 

 ters the reverse of those shown in the specimens preserved, while gener- 

 ally filled in by sand. Cases have been reported from Oswego County 

 near Fulton where small pebbles are mixed with the sand. 69 Such ar- 

 rangement could only indicate grooves filled by material spread over the 

 surface in which they were formed. Such grooves are difficult to explain 

 except as a series of tracks. These tracks would have a pronounced 

 median ridge and a series of sharp transverse ridges on either side of 

 this, separated .by concavities. There is no organism known in these 

 rocks capable of making such a track. A split caudal fin, used regularly 

 for propulsion, might perhaps account for this, as shown by Wood- 

 worth, 70 for the very similar, but larger trails, known as Climatichnites, 

 from the Potsdam sandstone of northeastern New York. If such a crea- 

 ture was an inhabitant of the sea, it is exceedingly strange thai no re- 

 mains have been found of it. If it was a land animal frequenting the 

 shores or the sand flats adjoining, we can more readily understand its 

 absence from these rocks, though we would at least suppose 1 thai an 



"Rochester Acad. Sci., 1000, vol. iv, p. 20.*?. 

 00 Vanuxem : Report of Third District, p. T.\. 

 70 New York State Museum Report, Bull. 69, 1008, p. 059, 



