Correspondence. 43 
formations from the upper Ordovician to the Esopus shale of the 
lower Devonian appear, with numerous fossils. At Otisville the 
Shawangunk grit is finely exposed in a large quarr\-. All the evi- 
dence at hand points to the conclusion that this formation, of a thick- 
ness of at least a thousand feet, was formed as a flood plain deposit. 
Its characteristics, except color, are the same as the New Jersey and 
Connecticut valley Jurassic sandstones. Ripplemarks, sun-cracks, cross- 
bedding, channel-fillings etc., are abundant. In the railroad cut west 
of Otisville the grit lies upon the Hudson shales, with coincident dip. 
On the contact there occurs a few inches of clay, next to the shale 
is quite free from pebbles, while next the grit it is filled with quartz 
pebbles. This was interpreted to be residual clay caused by the de- 
composition of the shale, through sub-aerial agencies, before it be- 
came covered by the grit. The old notions regarding rock formation 
required the presence of a body of water in which the sediments 
might be deposited. Several of the geological subdivisions showed 
characters which would not liave been present had these formations 
been laid down under water, for this mode of origin results in a 
sorting of the rock-forming materials, and no sorting is detected in 
these grits. Flood plain deposits are very irregular, both as to strati- 
fication and sorting of materials, and these features are well exhibited 
in the grits. Other formations that are probably flood-plain deposits 
are parts of the Potsdam sandstone in eastern New York, the Medina 
sandstone, the sandstones of the Catskill group, and many of the 
sandstones of the coal mesures of Pennsylvania and the Mississippi 
valley — in fact the geater part of the "'barren measures." 
Dr. Theodore G. White described his detailed study of the faunas 
of successive strata of the Lowern Ordovician in the Glens Falls, N. V.. 
section, and their relations to similar studies along the lake Cham- 
plain valley to the north, and the Mohawk and Black River valleys 
to the west. The section forms a low anticline along the shore of 
the Hudson. At the base is seen the Calciferous sandrock, con- 
taining Ophilcta and fucoids. Conformable upon this is a layer a 
few inches thick, of barren black shale, which is very much crushed, 
and then the same beds of the ostracod. Lepcrditia, and their asso- 
ciated corals and peculiar forms of Strophomena, as have been found 
in the lowest Black River zones on Button island in lake Champlain. 
The zones of Parastrophia and Triplcsia occuring near this portion 
of the series in localities to the north and west, were not found here. 
The succeeding coral beds of Coluiiniaria were well developed. Above 
these are the cross bedded gray beds, which in some recent report 
have been considered to represent the Birdseye limestone, which 
seems to be lacking in this locality, unless met with at this unex- 
pectedly high position. The upper portion of the section, which is of 
lower Trenton age, shows no unusual forms. The tendency of the 
lowest and the uppermost portions of the Ordovician sections in the 
region to wear away and appear wanting, owing to their, prevailing 
softness, was oonunentcd on. 
