THE GLACIAL PERIOD. 297 
The striking peculiarity of these terrace deposits is that they suddenly disap- 
pear at an elevation of 1050 or 1075 f^^t above tide, not a single rounded and 
transported boulder ever being found above the latter horizon, though occurring 
in countless numbers below this level. 
The hills along the river often rise 300 or 400 feet higher than the upper 
limit of the deposits, so that there can be no mistake about the elevation at 
which the terrace deposits disappear. The composition of these great heaps of 
surface debris is, along the immediate valley of the river, a heterogeneous mix- 
ture of sand, clay, gravel, rounded boulders of sandstone of every size, from an 
inch in diameter up to four feet, pieces of coal, leaves, logs of wood, and every 
other species of rubbish usually transported by streams. Back from the channel 
of the river, however, and especially where the surface configuration would make 
quiet water, there occur thick deposits of very fine, bluish white clay, in which 
great numbers of leaves are most beautifully preserved. These clays have been 
extensively used for the manufacture of pottery at Geneva and Greensboro, Pa,, 
and also to some extent at Morgantown and Fairmont, W. Va. Though the 
clay deposits occur at nearly every horizon they are purest near the upper Hmit 
of the terraces, and these are consequently the only ones that have hitherto been 
much explored. 
In the vicinity of Morgantown, terraces of transported material occur at the 
following approximate (measured by barometer) elevations : 
Feet above Feet above 
River. Tide. 
First terrace 30 800 
Second terrace , 75 865 
Third terrace 175 965 
Fourth terrace. . 200 990 
Fifth terrace 275 1065 
The accompanying cross section of the Monongahela valley, near Morgan- 
town, exhibits the relations of the terrace deposits to each other and to the river 
channel. 
The first terrace is the present flood plain of the river, consisting principally 
of fine sand, mud and gravel. It seems to possess some respectable antiquity, 
however, since Mr. Walter Hough, one of my students, dug some teeth and 
bones from five feet below its top, which were identified by Prof. O. C. Marsh as 
the remains of a species of peccary, an animal that has not inhabited the region 
in question within the American historic epoch. 
All of the other terraces have thick deposits of transported material wherever 
the original contour of the surface has favored its preservation from erosion. 
From the top of the fourth terrace Mr. Keck dug a well through seventy feet of 
clay, gravel and boulders without finding bed-rock. He also encountered logs of 
wood in a soft or semi-rotten condition near the bottom. 
Many other wells on the third terrace have been sunk to depths of twenty 
and thirty feet without reaching bed rock. 
