18 
AMERICAN GEOLOGY. 
From the foregoing facts it follows that rocks are now form» 
ing. 1 he muddy sediments, or the sand and gravel, will in 
time consolidate. There are, however, no additions made to 
the earth’s crust: the gain of one place is at the expense of 
another. The contribution which the mountains make to the 
plains, and to the ocean’s bottom, is from their tops and sides; 
and though the plains are raised, the mountains are lowered. 
§ 16. Water moving in masses, as in waves, modifies the 
character of the earth’s surface. It is upon and near the shore 
that waves produce the greatest modifying effects. The long 
swell of waves, as they break successively upon a shore, raises 
the mud and fine sand, and bears it onwards to the land. The 
material, whatever it may be, will accumulate in ridges, which 
have a steeper slope on the land than upon the ocean’s side. 
But ridges are formed also upon the shores of lakes on a scale 
commensurate with their size. As examples of ridges upon a 
large scale, I may cite Long island and its parallel outer oceanic 
ridge, and the ridge upon the south side of lake Ontario. These 
ridges are formed by the waves which bear some of the sand 
to its crest, when it falls over it to the land side. This is a 
permanent addition to the ridge. The ancient shores of lake 
Champlain, in Clinton county, may be traced by similar ridges 
of sand and gravel. There are no less than four nearly parallel 
ridges, which mark the former positions of the lake. These 
show that the land for long periods occupied positions at lower 
levels than at the present time, and that these changes of level 
have occurred since the drift period. There is generally 
towards the land a sheet of shoal water, which becomes a 
marsh, and which in time may be filled up. 
Water moving in mass, in the form of tides, modifies also 
the earth’s surface. The tide entering the mouth of a river 
flows up its channel, but meeting the down current of the river, 
it checks its flow. Some of its burthen of mud falls to the bot= 
tom, and forms .a bar or a shoal. The outward tide, however, 
receives the rest of the burthen, and bears it oceanward, some 
of which may be carried to the ocean rivers. The tide of our 
