METAMORPHISM OF ROCKS. 149 



extensive manufacturing establishments. The 

 steam which has been so ingeniously applied to 

 the evaporation and concentration of boracic 

 acid will probably hereafter, instead of wasting 

 itself in the air, be employed to move large 

 engines, which will be directed to the infinite 

 variety of production which engages the atten- 

 tion of labouring and intelligent artizans; and 

 thus, in course of time, there can be little 

 doubt that these lagoons, which were fled from 

 as objects of danger and terror by uninstructed 

 man, will gather round them a large intelli- 

 gent population, and become sources of pros- 

 perity to innumerable individuals." 



At all periods the earth's crust has ' been in- 

 cessantly under the influence of the powers of 

 chemistry within; and, consequently, the cha- 

 racter of its constituents has been constantly 

 undergoing remarkable changes. The peculiar 

 process, called by geologists the metamorphism 

 of rocks, is a striking illustration of this. In 

 various parts of the earth's crust there is evi- 

 dence of a heated mass of rock having been 

 pushed up from below completely through the 

 overlying beds. Such rocks are called Eruptive. 

 Their temperature at the time when they broke 

 through the overlying or sedimentary beds must 

 have been very great; probably not less than 

 1,000 Fahrenheit. The result of the application 



