Disintegration 

 Distances 



SCIENTIFIC SIDE-LIGHTS 



178 



carried on from the crests of the moun- 

 tains down to the sea, and in every latitude 

 under the sun. No exposed rock-surface es- 

 capes attack. In parched deserts as in well- 

 watered regions, in the dreary barrens of the 

 far north as in the sunny lands of the south, 

 at lofty elevations as in low-lying plains, the 

 work of rock-waste never ceases. Here it is 

 insolation that is the most potent agent of 

 destruction ; there it is rain aided by humus 

 and carbonic acids; or rain and frost com- 

 bine their forces to shatter and pulverize 

 the rocks. In latitudes where frost acts 

 energetically, the most conspicuous proofs 

 of rock-waste are the sheets and heaps of 

 debris that are ever traveling down moun- 

 tain slopes, or gathering at the base of cliff 

 and precipice. In lower latitudes the most 

 impressive evidence of disintegration is the 

 great thickness attained by rotted rock in 

 positions where it is not liable to be readily 

 swept away by running water. GEIKIE 

 Earth Sculpture, ch. 2, p. 29. (G. P. P., 

 1898.) 



868. 



Heat and Cold Break 



Down Wind Scatters in Dust. Rocks at 

 the surface are everywhere subject to 

 changes of temperature warmed by day 

 and during summer, cooled at night and dur- 

 ing winter. Thus they alternately expand 

 and contract, and this tends to disintegra- 

 tion, for the materials of which they are 

 composed often yield unequally to strain or 

 tension. In the rocky deserts of tropical 

 and subtropical regions, bare of verdure 

 and practically rainless, the effects produced 

 by alternate heating and cooling are very 

 marked. The rocks are cracked and shat- 

 tered to a depth of several inches; the sur- 

 faces peel off, and are rapidly disintegrated 

 and pulverized. Wind then catches up the 

 loose material and sweeps it away, leaving 

 fresh surfaces exposed to the destructive ac- 

 tion of insolation. More than this, the grit, 

 sand, and dust carried off by the wind are 

 used as a sand-blast to attack and erode the 

 rocks against which they strike. GEIKIE 

 Earth Sculpture, ch. 2, p. 23. (G. P. P., 

 1898.) 



869. DISORDERS OF SOCIETY 

 FROM TRANSGRESSION OF NATURAL 

 LAW Evil Points the Way to Betterment. 

 Is it vain to hope that the thoughtfulness 

 and candor which have been the natural in- 

 heritance of a few may yet be more common 

 among all educated men? The whole consti- 

 tution and course of things would receive an 

 earlier fulfilment did we carry about with 

 us an habitual belief in the inexhaustible 

 treasures which it holds in the power of 

 the agencies which it offers to knowledge 

 and contrivance. For then the results of 

 natural consequence would be accepted for 

 that which they teach, and not simply sub- 

 mitted to for that which they inflict. The 

 disorders of society would not so often be 

 supinely regarded as the result of inevitable 

 laws, but would be seen as the fruit always 



of some ignorance or of some rebellion; and 

 so the exhilarating conviction would be 

 ours that those disorders are within the 

 reach of remedy through larger knowledge 

 and a better will. ARGYLL Reign of Law, 

 ch. 7, p. 229. (Burt.) 



87O. DISPERSAL OF PLANTS 



Effected by Animals. Sometimes an express 

 provision is found in the structure of seeds 

 to enable them to adhere firmly by prickles, 

 hooks, and hairs, to the coats of animals, 

 or feathers of the winged tribe, to which 

 they remain attached for weeks, or even 

 months, and are borne along into every 

 region whither birds or quadrupeds may 

 migrate. Linnaeus enumerates fifty genera 

 of plants, and the number now known to 

 botanists is much greater, which are armed 

 with hooks, by which, when ripe, they ad- 

 here to the coats of animals. ... A deer 

 has strayed from the herd when browsing 

 on some rich pasture, when he is suddenly 

 alarmed by the approach of his foe. He in- 

 stantly takes to flight, dashing through 

 many a thicket, and swimming across many 

 a river and lake. The seeds of the herbs and 

 shrubs which have adhered to his smoking 

 flanks are washed off again by the waters. 

 The thorny spray is torn off, and fixes itself 

 in its hairy coat, until brushed off again in 

 other thickets and copses. LYELL Princi- 

 ples of Geology, ch. 37, p. 624. (A., 1854.) 



871. 



Effected by Man. 



Besides the plants used in agriculture, the 

 numbers which have been naturalized by ac- 

 cident, or which man has spread uninten- 

 tionally, are considerable. One of our old 

 authors, Josselyn, gives a catalog of such 

 plants as had, in his time, sprung up in 

 the colony since the English planted and 

 kept cattle in New England. They were two- 

 and-twenty in number. The common net- 

 tle was the first which the settlers noticed; 

 and the plantain was called by the Indians 

 " Englishman's foot," as if it sprung from 

 their footsteps. LYELL Principles of Geol- 

 ogy, ch. 37, p. 625. (A., 1854.) 



872. DISPERSAL OF SEEDS GRAD- 

 UAL Nature's Thrashing-machine Balls of 

 Buttomvood. The fruit of the buttonwood, 

 or sycamore, which grows along streams, 

 is in the form of balls an inch and a half 

 in diameter. These balls grow on the tops 

 of the highest branches, and hold on into 

 winter or longer. The stems are about two 

 inches long, and soon after drying, through 

 the action of the winds, they become very 

 flexible, each resembling a cluster of tough 

 strings. The slightest breeze moves them, 

 and they bob around against each other and 

 the small branches in an odd sort of way. 

 After so much thrashing that they can hold 

 no longer, the little nuts become loosened 

 and begin to drop off a few at a time. Cer- 

 tain birds eat a few and loosen others, which 

 escape, . . . each supplied with a ring 

 of bristles about the base, which acts as a 



