GLACIAL DAMS, LAKES, AND WATERFALLS. 377 



ginning of the Tertiary period. But, that no such length of 

 time can have elapsed since these upper terraces were depos- 

 ited, may be inferred from their structure and situation in 

 various other places. For example, vegetable and animal 

 remains of recent species are found in a very fresh state of 

 preservation in river deposits of the Ohio Valley correspond- 

 ing in age with the terraces in question. 



The first instance of this to be mentioned is one which 

 has been carefully investigated and described by Professor 

 I. C. White, and occurs on the Monongaliela River, near 

 Morgantown, W. Ya. The trough of the Monongaliela, 

 which joins the Alleghany at Pittsburg to form the Ohio, 

 is in every way similar to that of the Alleghany, with the 

 single exception that the terraces which line its banks at 

 heights corresponding to those of the Alleghany and upper 

 Ohio, contain no pebbles of northern drift, but consist wholly 

 of material which is native to the valley itself. At numer- 

 ous places along the Monongaliela there are extensive depos- 

 its of pebbles and bowlders from two hundred to three hun- 

 dred feet above the river, especially near where tributaries 

 enter. In many of these deposits there is nothing to indi- 

 cate their age ; but, at Morgantown, W. Va., there would 

 seem to be a decisive case, showing the comparatively recent 

 date of the deposition of this series of terraces. The follow- 

 ing is Professor White's description : 



Owing to the considerable elevation — 275 feet — of the fifth 

 terrace above the present river-bed [in the vicinity of Morgan- 

 town], its deposits are frequently found far inland from the 

 Monongahela, on tributary streams. A very extensive deposit 

 of this kind occurs on a tributary one mile and a half north- 

 east of Morgantown ; and the region, which includes three or 

 four square miles, is significantly known as the " Flats." The 

 elevation of the "Flats" is 275 feet above the river, or 1,065 

 feet above tide. The deposits on this area consist almost en- 

 tirely of clays and fine, sandy material, there being very few 

 bowlders intermingled. The depth of the deposit is unknown, 

 since a well sunk on the land of Mr. Baker passed through 



