ne 
= , = 
Pang II. Snor. iii. §3.] VEGETABLE FORMATIONS. 457 
wise by the tangles and smaller fuci which, growing abundantly 
on the littoral zone, break the force of waves, or diminish the effects 
of ground swell. 
4, Forests and brushwood protect soil, especially on slopes, from 
being washed away by rain. ‘This is shown by the disastrous results 
of the thoughtless destruction of woods. According to. Reclus,’ in 
the three centuries from 1471 to 1776, the “ vigueries,” or provostry- 
districts of the French Alps, lost a third, a half, and even three- 
fourths of their cuitivated ground, and the population has diminished 
in somewhat similar proportions. From 1836 to 1866 the depart- 
ments of Hautes and Basses Alpes lost 25,000 inhabitants, or nearly 
one-tenth of their population—a diminution which has with plausi- 
bility been assigned to the reckless removal of the pine forests, 
whereby the steep mountain sides have been washed bare of their 
soil. ‘The desiccation of the countries bordering the eastern Mediter- 
‘ranean has been ascribed to a similar cause.” 
5. In mountain districts pine forests exercise also an important 
conservative function in preventing the formation or arresting the 
progress of avalanches. In Switzerland some of the forests which 
cross the lines of frequent snow-falls are carefully preserved. 
Animals do not exert any important conservative action upon 
the earth’s surface, save in so far as they form new deposits, as will 
be immediately referred to. In the prairie regions of Wyoming and 
other tracts of North America, some interesting minor effects are 
referable to the herds of roving animals which migrate over these 
territories. ‘The trails made by the bison, the elk, and the big-horn 
or mountain-sheep are firmly trodden tracks on which vegetation will 
not grow for many years. All over the region traversed by the bison 
numerous circular patches of grass are to be seen which have been 
formed on the hollows where this animal has wallowed. Originally 
they are shallow depressions formed in great numbers where a herd 
of bisons has rested for a time. On the advent of the rains they be- 
come pools of water; thereafter grasses spring up luxuriantly, and so 
bind the soil together that these grassy patches, or “ bison-wallows,” 
may actually become slightly raised above the general level if the 
surrounding ground becomes parched and degraded by winds.° 
§. 3. Reproductive Action. 
Plants.—Both plants and animals contribute materials towards 
new geological formations, chiefly by the aggregation of their remains, 
partly from their chemical action. ‘Their remains are enclosed in 
deposits of sand and mud, the bulk of which they thus help to 
1 La Terre, p. 410. 
? Recent attempts to reclothe the dessicated stone-wastes of Dalmatia with trees 
have been attended with success. See Mojsisovics, Jahrb. Geol. Reichsanst. 1880, 
p. 210. 
* Comstock in Captain Jones’ “ Reconnaissance of N.W. Wyoming,”’ 1875, p. 179. 
