Page:The American Cyclopædia (1879) Volume XVI.djvu/519

 WATER These various sulphides result from the redu- cing action of organic matters on sulphates, and the most strongly sulphuretted waters are gen- erally gypseous and but feebly saline. An ex- cess of carbonic acid is also frequently met with in saline and in alkaline waters, which are sometimes so highly charged with it as to be acidulous to the taste and sparkling, as is the case of the Saratoga waters. It seems however to be an accidental ingredient, absorbed by the waters at considerable depths under pressure, and is wanting in the greater number of these saline springs. Waters coming from consider- able depths in the earth are found to have a more or less elevated temperature, and are des- ignated thermal waters, a name which proper- ly belongs to all such as are warmer than the mean annual surface temperature of the local- ity. The temperature of the solid crust of the earth increases on an average about 1 F. for each 60 ft. in depth, as has been shown in the water from deep artesian wells, and it is hence concluded that the waters of hot springs come from very considerable depths. Those of Vir- ginia and of Arkansas are well known, but those of the Yellowstone park are still more remarkable. Numerous springs of this region have temperatures varying from 160 to 200 F., a point above that of the ebullition of water in this elevated region. Hence the hot- ter of these waters on coming to the surface disengage vapor with explosive violence, giving rise to the phenomenon of geysers. These, like many other hot springs, hold in solution large quantities of silica, which they deposit at the surface, a fact which has been observed in similar waters in Nevada and in Iceland. The geological significance of such waters is very great, inasmuch as they give us some notion of the potent agencies which are at work in the deeper portions of the earth's crust, where the solvent action of the waters, exalted by heat and by pressure, is exerted upon alka- liferous rocks, giving rise to solutions which in their turn possess solvent powers far greater than those of pure water. Various experi- ments by recent investigators throw light on these actions of heated water and watery solu- tions. Thus it has been found that sulphate of baryta, when heated and cooled in presence of solutions of alkaline bicarbonates under pres- sure, is dissolved and redeposited in a crystal- line form. Silica under similar conditions dis- solves and crystallizes again in the form of quartz, and various metallic sulphurets have in like manner been obtained in crystalline forms, like those found in nature, and by reactions between their constituent materials, crystalline feldspar, mica, and pyroxene have been pro- duced. While these reactions take place rapid- ly at temperatures considerably above the boiling point of water, and in fact approaching a red heat, other observations have shown that very similar processes, resulting in the produc- tion of many of these mineral species, may take place more slowly at temperatures much WATER BUG 499 lower. Examinations of the baths at Plom- birea, Luxeuil, and Bourbonne-les-Bains in France have shown in the old constructions, which date from the Romans, the occurrence of crystalline calcite, fluor spar, and various sili- cates belonging to the class of zeolites, which have been generated by the long continued action of alkaline waters at temperatures from 140 to 160 F. upon the bricks and mortar; while coins and medals have given rise to well crystallized metallic sulphurets of various species identical in form and in composition with those met with in mineral veins. These observations throw great light on the phenom- ena of metalliferous veins, in which all the various minerals named, together with many more, are met with, arranged in such a manner as to show that they have been deposited as incrustations on the walls of fissures, which daubtless served as channels for the passage of heated waters. These, ascending toward the surface, where a diminished pressure ex- ists, have yielded up in crystalline forms their dissolved materials, thus in time filling up the fissures with a veinstone often charged with metallic ores. It has been shown that the hot springs in Nevada are even at the present time depositing silicious matters mingled with me- tallic sulphurets. A comparison between such lodes as those just described, in which the vein- stone may be carbonate of lime, sulphate of baryta, or quartz, occasionally with silicates like mica and feldspar, and granitic veins, which are essentially composed of these latter mineral species with quartz, leads to the con- clusion that these veins have been formed in a similar manner, and in fact that the elements of those granites which occur in veins have in like manner been at one time in solution. It is difficult to draw the line between these and the larger masses of granitic rocks, in the pro- duction of which water has doubtless inter- vened under conditions of which we have but an imperfect conception. The crystals of quartz and of various other minerals in gran- ites are found to contain minute cavities whol- ly or partially filled with water, often holding saline matters in solution ; and it is supposed that in the case of eruptive granites, as in lavas, water has played an important part in giving liquidity to the rock. (See GEOLOGY, GBAMTK, and VOLCANO.) For the natural history of water, see Bischof, LehrbucJi der chemischen und pTiyaiTcalischen Geologic (2 vols., 1847-'54; English translation, 1854-'9) ; Lersch, Hydro- chemie (Berlin, 1864); and Hunt, "Chemical and Geological Essays" (Boston, 1875). WATER BUG, the popular name of the hemip- terous insects of the suborder heteroptera, and families notonectida and neparia. In this sub- order the anterior portion of the first pair of wings is of a horny consistence ; the antenna? are very small, of three or four short joints, and concealed beneath the eyes. In the noto- nectida the head is rounded, and as wide as the thorax ; the common boat flies of America and