ice. 687 



open at both ends and of great breadth and depth, so as to allow the 

 oceanic currents to sweep through. 



As the submergence progressed, there would be, through wave- 

 action, extensive degradation of the ridges and mountains over the 

 surface, and a distribution of the detritus through the intervening de- 

 pressions. In a subsequent emergence of the land, the mountains and 

 ridges would be still further degraded, and the valleys filled by their 

 debris. The laws of sea-coast action would again come into play, and 

 the wear of all new headlands, and the filling of bays, continue to be 

 the result, so long as the emergence was in progress. 



If the continent were to a large extent without mountains as was 

 the fact in early geological time, the broad flat surface might then lie 

 slightly above or below the tide-level at once, or nearly simultaneously, 

 so that, under a small change of level, the waves could sweep across 

 the whole area and the deposits might have a continental extent. 

 Through continental oscillations, causing slight emergences of large 

 areas to alternate with varying submergences, variations in the forma- 

 tions would be produced, differences of depths and differences of cur- 

 rents causing transitions from arenaceous to argillaceous or to pebbly 

 accumulations, or to clear waters fitted for corals and the other life 

 which has contributed to limestone making. 



3. FREEZING AND FROZEN WATER. 



Water performs part of its geological work in the act of freezing, 

 and another part when frozen, in the condition of snow and ice. 



1. Water Freezing. 



Rending and Disintegration from Expansion. — Water has its great- 

 est density at 39°-2 F. (4° C.) On cooling below this it gradually 

 expands ; and on becoming ice, at 32° F., it has increased in volume 

 1-1 lth, or lineally, l-35th, and diminished in density to 0*92. 



Hence if freezing tak< j s place in crevices, it opens and deepens them, 

 and thus carries on a process of destruction. It tears to pieces rifted, 

 jointed, and laminated rocks, separating often large masses ; and as 

 almost all rocks absorb moisture at surface, if not also throughout the 

 mass, there are few that do not suffer some disintegration when ex- 

 posed to icy weather. In cold latitudes rocky bluffs have usually, 

 from this source, a long talus of broken stone, while, in the tropics, 

 they are generally free from fragments. This kind of degradation has 

 produced much of the soil and drift material of the globe. 



As a body of water 35 feet wide will make 36 feet in width of ice, 

 the freezing of the surface of small ponds may bring pressure against 



