RIVER TERRACES. 101 



The beaches are represented by two colors one for the Champlain clays which include some of the lower 

 beaches, and another for the more elevated gravel and sand beds which as yet have aiforded no marine relics. 

 No distinction is attempted to be made between the higher and lower beaches of the latter character, though 

 their difference of level is quite great at some localities. 



Modified Drift is embraced under six forms : River Terraces, Lake Terraces, Maritime Terraces, Moraine 

 Terraces, Beaches and Sea Bottoms. 



I. RIVER TEERACES. 



These are the most perfect of all, and are found along the shores of almost all rivers, 

 but especially those passing through hilly countries, and forming narrow basins with a 

 succession of gorges. River terraces may be subdivided into four varieties, differing in 

 position, and probably, also, in their mode of formation. 



1. The Lateral Terrace. This is the ordinary terrace which we meet along the banks 

 of a river, often many miles in length, and sometimes even miles in width. 



2. The Delta Terrace. This occurs at the mouths of tributary streams, and was most ob- 

 viously a delta of the tributary, but as the waters sunk, the delta was left dry, and the 

 tributary cut a passage through it, so as to form a terrace of equal height on opposite banks. 



3. Tlie Gorge Terrace. This occurs either above or below the gorges of a stream, and is 

 intermediate between the lateral and delta terraces, graduating into both. 



4. TJie Glacis Terrace. This is not level-topped, but slopes gradually both ways from 

 its axes on the side next the stream much more rap- 

 idly than on the other. Outwardly it resembles the 



glacis of a fortification, and hence the name. It is 

 usually found in alluvial meadows, and might perhaps 

 be regarded as merely the uneven surface of a lateral 

 terrace, as it is seldom more than a few feet high. The 



true types of the glacis terrace are found in South America, as described by Charles 

 Darwin, and among the Alps, where broad terraces slope very rapidly towards the stream 

 to its very brink. Fig. 46 represents one of the best examples of this kind of terrace found 

 in Vermont. The sketch is taken from the Illustrations of Surf ace Geology, Plate II., No. 31, 

 and the originals are found near the mouth of Saxton's River, just below Bellows Falls. 

 They are laid down accurately the heights above Connecticut River, respectively, 35 feet 

 and 34 feet; their thickness, respectively, 10 feet and 12 feet; and their length, respectively, 

 14 rods and 16 rods, all being given as determined by leveling. On Fig. 54 they may 

 be seen in their relations to a much larger section crossing the valley. It will be seen 

 that they constitute merely undulating portions of the lowest terrace, and perhaps ought 

 not to be considered as distinct terraces. Yet they are sometimes of considerable height, 

 and deserve notice, because they show us one of the modes in which nature accumulates 

 terrace materials. The method of their formation will be considered elsewhere. 



II. LAKE TERRACES. 



These scarcely differ from the lateral terraces of rivers. Indeed, many small lakes, and 

 even some of the larger ones, appear to have been merely expansions of rivers, such as 

 are now seen in great numbers in the basin of the upper Mississippi, west and southwest 



