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AT2 “DYNAMICAL GEOLOGY. — [Boox Tif 
of moor and bog into cultivated land, and the clothing of bare hill- 
sides with green crops or plantations of coniferous and hardwood 
trees. - , 
2. On the Flow of Water.—(1) By increasing or diminishing 
the rainfall man directly affects the circulation of water over the — 
land. (2) By the drainage operations which cause the rain to run 
off more rapidly than before, he increases floods in rivers. (35) By 
wells, bores, mines, or other subterranean works, he interferes with 
underground waters and consequently with the discharge of springs. 
(4) By embanking rivers he confines them to narrow channels, some- 
times increasing their scour, and enabling them to carry their 
sediment further seaward, sometimes causing them to deposit it over 
the plains and raise their level. 
3. On the Surface of the Land.—Man’s operations alter the 
aspect of a country in many ways :—(1) by changing forest into bare 
mountain, or clothing bare mountains with forest; (2) by promoting 
the growth or causing the removal of peat-mosses ; (3) by heedlessly 
uncovering sand-dunes, and thereby setting in motion a process of 
destruction which may convert hundreds of acres of fertile land 
into waste sand, or by prudently planting the dunes with sand- 
loving herbage or pines, and thus arresting their landward progress ; 
(4) by so guiding the course of rivers as to make them aid him 
in reclaiming waste land, and bringing it under cultivation; (5) 
by piers and bulwarks, whereby the ravages of the sea are stayed, 
or by the thoughtless removal from the beach of stones which the 
waves had themselves thrown up, and which would have served for 
a time to protect the land; (6) by forming new deposits either 
designedly or incidentally. The roads, bridges, canals, railways, 
tunnels, villages, and towns with which man has covered the surface 
of the land will in many cases form a permanent record of his 
presence. Under his hand the whole surface of civilized countries 
is very slowly covered by a stratum, either formed wholly by him, or 
due in great measure to his operations, and containing many relics 
of his presence. ‘I'he soil of old cities has been increased to a depth 
of many feet by the rubbish of his buildings; the level of the 
streets of modern Rome stands high above that of the pavements of 
the Ceesars, and this again above the roadways of the early republic. 
Over cultivated fields potsherds are turned up in abundance by the 
plough. The loam has risen within the walls of our graveyards, as 
generation after generation has mouldered there into dust. 
4. On the Distribution of Life.—It is under this head, 
perhaps, that the most subtle of human influences come. Some of 
man’s doings in this domain are indeed plain enough, such as the 
extirpation of wild animals, the diminution or destruction of some 
forms of vegetation, the introduction of plants and animals useful to 
himself, and especially the enormous predominance given by him to 
the cereals and to the spread of sheep and cattle. But no such ex- 
tensive disturbance of the normal conditions of the distribution of 

