OCR Text |
Show CHAPTER XII. Difftlrence between the transporting power of springs and rivers-Many springs carry matter from below upwards-Mineral ingredients most abundant in springs-Connexion of mineral waters with volcanic phenomena-Calcareous springs-Travertin of the Elsa-Baths of San Vignone and of San Filippo, near Rauicofani-Spheroidal structure in travertin, as in English magnesian limestone-Bulicami of Viterbo-Lake of the Solfatara, near Rome-Travertin at Cascade of Tivoli-Ferruginous Springs-Cementing and colouring property of iron-Brine Springs-Carbonated Springs-Disintegration of Auvergne granite-Caverns in limestone-Petroleum Srrings-Pitch Lake of Trinidad. WE have hitherto considered the destroying and transporting power of those atmospheric waters which circulate on the surface of the land ; but another portion which sink deep into the earth, present phenomena essentially different in character. Rivers, as we have seen, remove earthy matter from higher to lower levels, but springs not only effect this purpose, but sometimes, like volcanos, carry matter from below upwards. Almost all springs are impregnated with some foreign ingredients, which render them more agreeable to our taste, and more nutritive than pure rain water ; but as their mineral contents are in a state of chemical solution, they rarely, even when in great abundance, affect the clearness of the water, and for this reason, we are usually unconscious of the great instru· mentality of these agents in the transfer of solid matter from one part of the globe to another. 'l'he specific gravity of spring water being greater than that of rain, it augments the carrying power of rivers, enabling them to bear down a greater quantity of matter in mechanical suspension towards the sea. Springs, both cold and thermal, rise up beneath the waters of lakes and seas, as well as in different parts of the land, and must often greatly modify the mineral character of subaqueous deposits. The number of metals, earths, acids, and alkalies, held in solution by different springs, comprehends a considerable portion of all known substances, and recent observations have tended continually to augment the list; but those alone which are ORIGIN 01? 'I'll.·.,~ RMAL SPRINGS. (9~ most abundant, need be reO'ard d f . . 'l'hese are lime, ir01~ maO'no . e . 1~s 0 geologwal Importance; . ' o esia, SIIca alum· d carbomc and sulphuric acids. B 'd ' Ine, ~o a, and th~ leum, or liquid bitumen and 't esi .es these, sprmgs of pctro. · · ' 1 s vanous modifi · f mmcral pitch, naptha and as h I ca Ions, such as over the surface of the eartl pba tum, ar·e _largely distributed · h l, ut usually m c1 . wit volcanos. The relat' . d ose connexwn · IOn, m eed of I 11 · Impregnated copiously wi'tll m.m era1 m' attera tm os1t a sprmgs subterranean heat, seems placed b d 11 ' 0 t le sources of modern research M' I eyon a reasonable doubt by ' • mera waters as th r I b are most abundant in regions f' . e} lave een termed, ~arthquakes- are most frequent an~ vi:~tJve volca~os, or where 1s often very hiO'h and ha b k ent. Their temperature . o ' s een nown to b heightened or lowered by th h I f e permanently I e s oc { o an earthquake Th vo ume of wat.e r also given ou t h as b een so t' · Lr e by the same cause WI'th tl . me Imes auected . · 1e exceptiOn of T h . entermg most abundanti . t th . si Ica, t e mmerals differ from those in cJ;n o .' ermal r waters. do not seem to 'k' sprmO's, There 1 stri mg analoO'y betw th 0 s, moreover, a o een e earthy matt , 1 . gaseous s.t ate by volcanos ' and tll ose wI 1 erew1.cthrs se vo· ved· m h a same region are impreO'nated . d h prmgs m t e site of active to that o of t'. an wl en we proceed from the bo . ex met vo canos we fi d 1 ) a undmg in precisely the same kind ' . n t le atter thermal and mineral waters e f of sprmgs. Where I occur ~ar rom t · . vo canos, some great intern 1 d ac Ive or extinct invariably marks the 't al erangement in the strata almost SI e to 1ave been at · remote, the theatre of violent h k some penod, however S · eart qua es . prmgs, are in general 'b bl ' water through porous ro:k:sc~h;· e to tl~c percolatio~ of rain-laceous strata is thrown t' lch, meetmg at last with argil ... l'h d ' ou to t 1e surfa B · I oo ' they sometimes d d b .11 ce. ut, m all like-f b escen y ussures 1 o su terranean heat. Michell . . ' even to t le regions pent-up volcanic vapo I . 1' m 1760, suggested that those I urs w llC 1 caus ·th 1 a so through rents and . . , e eaJ qua {es, penetrate . cavitJes .. and d·' . nated with sulphurous d 'h uve up water Impreg- 1 an ot er matt h b are c larged with their . l . . ers, w ere y springs D1 • mmera InO'red1ents N · · . eans ltnprobabJe, that th o . . or IS It by any Is able to lift up I e same po\ver whiCh when intense he J· ght, should evena . co .u mn of ]a va many thousand feet in rau. s.m g to the sum m lts. more 1a ngm' d -State be capable of ace consi4erable_quantitie§ of water from the |