METAMORPHISM. . 759 



correspond to two quarts of water for every cubic foot of rock. As a 

 cubic inch of water at the ordinary atmospheric pressure will produce 

 nearly a cubic foot of steam, the amount was large in proportion to 

 the amount of rock, whatever the pressure ; and this would be true if 

 the proportion of water was half less. Under such circumstances at 

 high temperatures, steam was at hand ready for work at chemical and 

 other molecular changes. In general, the beds contained as stated 

 above, all the ingredients needed for their transformation into crystal- 

 line rock. 



But this water of the original sedimentary rocks may have been 

 oceanic water, which is mineral water, of indefinite distribution, 

 abounding in salts of soda and magnesia, and yielding also, in smaller 

 proportions, boracic acid, and many other ingredients. The ocean 

 made nearly all the sedimentary beds of the globe, and continued to 

 penetrate them as long as they remained beneath the sea-level un- 

 changed ; and further, it has left in many of them great deposits of its 

 sodium compound (common salt), with some of its magnesium and 

 borax compounds ; and briny waters are often given out when no 

 solid salt is present. If the ocean contained more of phosphates in 

 Archaean time than now (p. 593), or of any other ingredient, this also 

 would have been among the contributions of its waters. With sub- 

 aerial sedimentary beds, waters of mineral springs may have given 

 some ingredient, whenever they had a chance ; but these have taken 

 a larger part in local metamorphism than in regional. 



3. Effects of the heat and moisture. — Superheated steam is well- 

 known to be an exceedingly powerful chemical agent as a destroyer 

 of cohesion, a solvent, and a promoter of decompositions preparatory 

 to recompositions. 



Mr. J. Jeffrys, in 1840, subjected some feldspathic and other sili- 

 ceous minerals to a current of steam inside of a kiln made for vitrify- 

 ing brown stone ware, and with them a few articles of the stone ware. 

 At a full red heat, little effect was produced ; but above that of fused 

 cast iron, there was rapid erosion, and in ten hours, "more than a 

 hundred weight of mineral matter had been carried away in the va- 

 pors." Daubree has experimented with the direct object of making 

 silicates by means of superheated steam. Having put a little water 

 in a strong glass tube, and after closing it, subjecting it to a tempera- 

 ture of 750° F. for several weeks, he obtained, besides a hyd rated sili- 

 cate allied to the zeolites, quartz in well-defined crystals, and, in an- 

 other case, perfect crystals of the light-colored variety of pyroxene, 

 called diopside. A clay, from near Cologne, used in making crucibles, 

 heated in the glass tubes, became charged with scales of a mica or 

 chlorite (the quantity being too small for an analysis). Crystals of 



