TERRACE EPOCH. 561 



River into the Atlantic. Finally, by further retreat of the ice-foot, 

 they drained northeastward, as now, through the St. Lawrence River. 



3. Rivers. — It is hardly necessary to say that the re-elevation would 

 lay bare the old flood and estuary deposits of the rivers, and the rivers 

 would immediately commence cutting into these deposits, forming ter- 

 races and bluffs, in number and height depending upon the depth of 

 the cutting. The Connecticut River has made many of these terraces, 

 the highest, of course, being the oldest. The Mississippi has apparently 

 made but one, but this one is very high (Fig. 933). The highest point 

 of this Champlain deposit, according to Hilgard, is at least 450 feet 

 above tide-level, showing a re-elevation and a cutting to that extent 

 during the Terrace epoch. 



History of the Mississippi River. — It may be interesting to stop a 

 moment, and trace, briefly, the history of this great river. During the 

 Cretaceous period, the Ohio probably ran into the embay ment of the 

 Gulf, represented in Fig. 755 (p. 470) ; but the Mississippi probably 

 did not yet exist. The drainage of all that part of the continent was, 

 doubtless, into the great interior Cretaceous sea. At the beginning of 

 the Tertiary period, the Mississippi probably commenced to run into 

 the Tertiary embayment, shown in Fig. 844 (p. 505). The Red and 

 Arkansas, if they then existed, were not tributaries, but separate rivers, 

 emptying into the same embayment. The Ohio was almost, if not 

 quite, a separate river also. During the early Glacial epoch, the whole 

 embayment of the Gulf was abolished by elevation. This is clearly 

 demonstrated by the torrential pebble-deposit (Orange sand), and by 

 the stump-layer (old forest-ground), found by Hilgard beneath the 

 Port Hudson (Champlain) deposit, on the shores of the Gulf. During 

 the same epoch, by reason of this elevation, the great trough, represented 

 in Fig. 933, was scooped out of the Tertiary strata, 200 to 500 feet 

 deep, by the erosive power of water, favored by the greater slope of the 

 country southward at that time, and also by the greater water-supply. 

 During the Champlain epoch, by subsidence this great trough became 

 an arm of the Gulf, or an estuary, fifty to one hundred miles wide, and 

 reaching up to the mouth of the Ohio, with extensions up the tribu- 

 taries ; and this estuary became filled, 200 to 500 feet deep, with sedi- 

 ments. This deposit was at first estuarian (Port Hudson), and after- 

 ward river-silt (Loess). At the same time the Mississippi was con- 

 nected with the Great Lakes, then greatly enlarged, and with Lake 

 Winnipeg, then also greatly enlarged, as Lake Agassiz. During the 

 Terrace epoch, this silt was laid bare, and the river commenced and 

 continued to cut, until the bluffs became 200 to 400 feet high. Finally, 

 during the Recent epoch, the river has again commenced building up 

 by sedimentation, showing thus a slight depression again, or at least 

 a cessation, of the re-elevation of the Terrace epoch. This up-building 



