1895.] Geology and Paleontology. 477 
White) constitute the Hamilton stage; true Genesee shales and Tully 
limestones are wanting; the Chemung (of White) is found to be 
Lower Portage; beginning with the Starucca sandstones and New 
Milford red shales there is a series of deposits equivalent to the One- 
onta sandstones of New York; the line of demarkation between the 
Chemung and Catskill lies at the base of the sandstones overlying the 
Montrose shales; and, finally, the Mount Pleasant Conglomerate on 
the Pocono Plateau represents the base of the Pocono. 
The classification proposed by Prosser then would be as follows: 
Lower Car- 
j Pocono Mount Pleasant Conglomerate. 
boniferous 
Mount Pleasant Red Shale. 
Elk Mountain sandstone and shale. 
Catskill Cherry Ridge Group. 
Upper Honesdale sandstones. 
Devonian 
z Fortage (including Oneonta) (of Prosser). 
ey Chemung (of Prosser). 
Middle i Hamilton (Prosser). 
Devonian goarn Marcellus shales. 
Lower : : Upper Helderberg. 
Devonian sale pit Cauda-galli grit. 
The English Tarns.—While investigating the Tarns of Lake- 
land, England, with the view of determining their origin, Mr. J. E. 
Marr discovered that many basins supposed to be rock-bound were in 
reality not true rock-basins, although the streams issuing from them- 
run over solid rock close to the surface of the lake. The facts as ob- 
served by the authorare these: Some of the tarns were moraine-dam- 
med at the exit. Should the exit of the lake thus formed immediately 
overlie the old river-bed, the lake would have a brief existence, for 
the morainic material would soon be worn away. If, however, the low- 
est point of the morainic barrier did not lie vertically over the old 
river valley, the out-let stream would cut rapidly until it reached the 
level of the rock, and then in the majority of cases would cut sideways 
along the junction of the rock and the drift until it reached its original 
position, when the lake would be drained. But if a ridge of rock lay 
between the position attained by the stream issuing from the lake and 
the position of the former valley-bottom, denudation would be retarded, 
