550 



CENOZOIC TIME. 



A peat bed of the Alluvian era, a mile east of Germantown, Montgomery County, 

 Ohio, has been described by Prof. Edward Orton. 



The loess of the Mississippi contains numerous fresh-water shells, among them Palu- 

 dina ponderosa Say, Melania canaliculata Say, Cyclas rividaris Say, Cyclostoma lapi- 

 daria Say, Physa heterostropha Say, Limncea elongata Say, Planorbis bicarinata Say, 

 Valvata tricarinata Say, Unios, etc. 



5. Upper level of the terrace formations. — The height of the river- 

 border formations above modern flood-level often increases to the 

 northward — floods having been greater where the ice was thickest. 

 On the Connecticut, the height at Midclletown, Ct., is 150 feet ; at 

 Springfield, Mass., 180 feet; at Hanover, N. H., 240 feet. On Lake 

 Ontario and the Great Lakes the terraces are 300 to 500 feet high. 



But the level varies according to (1) the varying pitch of the bed, 

 (2) the varying width of the valley, and (3) any obstructions encoun- 

 tered, — increasing pitch and width of valley tending to diminish 

 height, and vice versa ; and obstructions (whether proceeding from a 

 narrowing of the valley, or from impediments due to rocky ledges in 

 the way, or to amount of detritus under transportation) causing a ris- 

 ing of the level of the floods, and therefore of the terraces or flood- 

 deposits. 



Again, where narrows existed at which transported ice or drift could 

 dam the stream, the terraces above the narrows have an extraordinary 

 height; and, then, below the narrows, there is a rapid fall off in level. 

 The height of 150 feet on the Connecticut at Middletown, was occa- 

 sioned by such a dam ; for south of the narrows the height decreases at 

 a mean rate of five feet a mile, and the height at the mouth of the 

 river, on Long Island Sound, is less than fifteen feet. Further, small 

 streams, receiving little water, would have had low terraces under any 

 circumstances. 



Stevenson has described very high broad terraces in Western Penn- 

 sylvania, the origin of which has not yet been fully explained. (Am. 

 Jour. Sci., 1878.) 



Heights of Upper Terraces, east of Rocky Mountains, above the level of rivers or lakes. 

 — On the coast, along the southern borders of New England, 10 to 25 feet. On the 

 Thames, in Eastern Connecticut, the terrace at its mouth is not distinct; 3 miles above, 

 near New London, the height is 25 feet; from there it rises 5 feet a mile to the narrows 

 below Norwich, where there must have been a dam, as on the Connecticut; and at Nor- 

 wich, above the narrows, the height of the plain is 100 to 117 feet. The sandy terrace 

 between Schenectady and Albany, N. Y., and opposite the latter place, east of the Hud- 

 son, is 330 to 335 feet above the river. On the Genesee, east of Portage, the upper 

 level is 235 feet above the river. 



The ridge road or terrace, south of Lake Ontario, 190 feet above the lake, the greatest 

 height (Hall); terrace south and southwest of Lake Erie, 220 feet; north of Lake 

 Ontario, at Toronto and other points, 30 to over 500 feet; the Davenport ridge, west of 

 Toronto, 250 to 300 feet; west of Dundas, west end of Lake Ontario, 318 feet (under the 

 escarpment of the Niagara formation, which is 100 feet higher); near Fredericton, New 

 Brunswick, on the St. Johns, 345 feet above the river; at other points below, on the 



