TEKKACED VALLEYS. 95 



are generally composed of the ruins of the higher terraces, modified, rounded and assorted 

 by currents of water. 



But there are often elevations and depressions in the highest terrace of a different char- 

 acter from the gullies and ravines excavated by rains and freshets, which seem to have 

 constituted the original surface of the terrace. They may be described as rounded or 

 curved elevations, with similar depressions ; which have been likened to a chopped sea, or 

 to the eminences and anfractuosities on the surface of the human brain. These elevations 

 and cavities could not have been made by water alone, for the depressions are basin- 

 shaped, and vary from ten to one hundred feet in depth, while the unbroken margins for- 

 bid the idea of the previous exit of any current from the depressions. Yet the materials 

 are often stratified and always water-worn. No level-topped terrace is ever found above 

 this terrace. These deposits are called moraine terraces. They form an interesting fea- 

 ture in the scenery of valleys, and are among the most difficult of all the phenomena of 

 Surface Geology to sketch satisfactorily. They will be referred to again, inasmuch as 

 similar phenomena are found away from rivers upon elevated plains and valleys. Their 

 place in valleys is shown in D, Fig. 39. 



5. Above the terraces, in our ascent from the river, we find other accumulations of 

 decidedly water-worn materials, generally coarser, the fragments of rolled and smoothed 

 rock being sometimes a foot or two in diameter, yet still more or less sorted. Coarse 

 sand, however, constitutes the greater part of the deposit, and sometimes the whole of it. 

 Its outline is rounded, rarely with a level top for any considerable thickness. Yet in its 

 longest direction it maintains essentially the same level, and often may be seen for many 

 miles at the same height, as a sort of fringe along the sides of the hills that bound a val- 

 ley, appearing as if these deposits once formed the beaches or shores of estuaries that 

 occupied those valleys. Such they are supposed to be, and are what will be described as 

 Ancient Sea Beaches. One is represented in the figure (E, Fig. 39) as skirting the side of 

 the valley near its border, and not extending far beneath the terraces, as it was formed 

 upon a shore. As we rise still higher, the materials are less rounded, and may have 

 formed beaches at higher levels, when less opportunity was afforded to the waters of wear- 

 ing away and comminuting the rocks. 



6. Passing beyond and above the terraces and beaches, thus lying at the bottom, and 

 along the sides of the valleys, we reach the genuine drift deposit (F, Fig. 39), consisting 

 of materials that are coarser, more angular, and less arranged in strata. These are 

 strewn promiscuously over the hills, except those quite steep, where the materials could not 

 find a resting place. They are also seen occasionally in the valleys, wherever the terraces 

 and beaches have been worn away or never existed. Yet it must be confessed that it is 

 often impossible to draw a line of distinction between the oldest beaches and the drift. 

 They pass insensibly the one into the other. The large blocks of the drift are indeed 

 frequently angular, but they are mixed with finer materials that have been ground down 

 and rounded, either by aqueous or glacial agency ; and the oldest beaches seem to be of 

 essentially the same materials, somewhat more modified. 



It is important, also, to mention that what appears to be genuine drift is sometimes 

 mixed with, and sometimes superimposed upon, the beach and terrace materials. This is 

 especially true of large erratic blocks. And it shows us that the drift agency, whatever 



