SURFACE GEOLOGY. 



3. Maritime Terraces. 



Perhaps I ought not to speak of terraces as existing on the margin of the sea, 

 but to regard all accumulations of sand and gravel there as beaches. Some of 

 these accumulations, however, are so nearly level-topped as not to differ from 

 genuine terraces, and this is the main distinction which I would make between 

 terraces and beaches. It is not, however, a distinction of much practical import- 

 ance. At the mouths of rivers, the two varieties are often seen running into each 

 other. 



Moraine Terrace. — I apply this term to a peculiar form, not unfrequently assumed 

 by the more elevated terraces, exhibiting great irregularity of surface; elevations 

 of gravel and sand, with correspondent depressions of most singular and scarcely 

 describable forms. I prefix the name moraine terrace to such accumulations, under 

 the impression that stranded ice, as well as water, was concerned in their production. 



Sea Beaches. 



The most perfect of these are seen along the sea-coast in the course of forma- 

 tion. They consist of sand and gravel, which are acted upon, rounded, and commi- 

 nuted by the waves, and thrown up into the form of low ridges, with more or less 

 appearance of stratification or lamination. As we rise above the terraces along 

 our rivers, and often on the sides of our mountains, we find accumulations of a 

 similar kind, evidently once deposited by water, and having the form of modern 

 beaches, except that they have been often much mutilated, by the action of water 

 and atmospheric agencies, since their deposition. These have hitherto been con- 

 founded with drift, but they nearly always lie above it, and show more evidently 

 the effects of some comminuting, rounding, and sorting agency — of water, indeed, 

 since this is the only agent that could produce such effects. They evidently belong- 

 to a period subsequent to the drift, and I cannot doubt that they once constituted 

 the beaches of a retiring ocean. The proof of this will be given further on. 



I have spoken of these beaches as lying above the terraces. I mean that they 

 are at a higher level often, but geologically they are lower. When terraces occur 

 as well as beaches, the latter always are seen at a higher level than the former ; 

 usually forming fringes along the sides of mountains. Yet in other places rivers 

 may exist at a much higher level, which have terraces also ; and usually above 

 them we find beaches, still retaining the same relative position to the terraces. 



General Liihological Character of the Terraces and Beaches. 



As a general fact, I give the following description, applicable to the terraces and 

 ancient beaches : — 



1. The most perfect terrace is an alluvial meadow, annually more or less over- 

 flowed, and increased by a deposit of mud or sand. Rarely are the materials as 

 coarse as pebbles, except on a small scale. Yet usually they are sorted, laminated, 

 and stratified. (See A on Fig. 1, Plate XI, which is an ideal section across a valley.) 



