46 CHANGES IN BOOKS. 



Pulverulent carbonate of lime, such as chalk and marl, readily becomes crystalline or saccharoid, by being 

 brought into a liquid condition, as is sometimes seen in the vicinity of trap dikes. 



Bischof contends that dolomite, which is a double carbonate of lime and magnesia, is produced whenever 

 there is " a permeation of carbonate of lime, by water containing bicarbonate of magnesia, which is one 

 of the most common constituents of spring water." Hunt, of the Canada Survey, maintains that 

 " dolomites, magnesites, and magnesia marls, have had their origin in sediments of magnesian carbonate, 

 formed by the evaporation of solutions of bicarbonate of magnesia ;" which solutions have resulted from 

 the decomposition of sulphate or chloride of magnesia by bicarbonate of soda. (Am. Journal Sci., 2d 

 Series, Vol. XXVIII., p. 383.) 



Serpentine and other varieties of rock that come under the general denomination of Ophiolites, are 

 essentially hydrous silicates of magnesia. Talc, chlorite, and steatite, have so nearly the same chemical 

 constitution, that they may easily pass, and doubtless have often passed, into one another more often 

 probably from the schists into the serpentine than the reverse ; and that too most likely in the wet way, 

 although the serpentine is usually as unstratified as granite, and sometimes has in it distinct veins of 

 chlorite as at Newfane, in Vermont. Greenstone, or diorite, also passes into serpentine, which is prob- 

 ably formed out of it. Hornblende, feldspar, and mica, have likewise been converted into serpentine. In 

 the very probable opinion of Sir William E. Logan, the abundant serpentines of the Green Mountain 

 range have resulted from changes in silicious dolomites and magnesites. Other minerals and rocks might be 

 named as capable of producing serpentine by metamorphosis ; such as garnet, olivine, chondrodite, gabbro, &c. 

 As it is one of the final products of mineral alteration, serpentine is one of the most permanent of rocks. 



Quartz rock, being insoluble by water or acid, "appears," in the opinion of Bischof, "in all cases to be 

 a product of the decomposition of silicates in the wet way." This opinion certainly seems plausible. 

 But when we examine the mountains of almost pure compact quartz, certainly 1000 or 2000 feet high, it 

 seems difficult to conceive how all the other ingredients could have been separated so entirely, and leave 

 the quartz in such enormous solid masses ; and hence we have suggested that some of it may have origi- 

 nated in silicious limestone. 



The changes that are found to have taken place in the ores of iron are a good example of metamorphism. 

 Starting with the carbonate, it is first changed into hematite, both hydrous and anhydrous ; next into 

 specular ore, and then into the magnetic protoxide. 



Carbonaceous matter affords another good example. Peat, which is partially decomposed vegetable 

 matter, is the first stage of the metamorphosis. This, permeated for ages by water, and covered by aqueous 

 deposits, will become lignite, or brown coal. The next step develops bitumen, even without much increase 

 of heat above the ordinary surface temperature. By still more powerful metamorphic action, the bitumen 

 disappears, and leaves anthracite. A further step in the process produces graphite, or black lead, and 

 perhaps the ultimate product is diamond. 



Change of slate, schistose rocks, conglomerates and breccias, into granitic rocks is metamorphism. Theory 

 makes such changes quite possible and probable, and observation shows that they have been made, of which 

 we have already given examples and details. 



The following statements may be regarded as inferences from the doctrines of metamorphism as above 

 developed. 



1. We see how it is that azoic schists may be mterstratijied with fossiliferous strata. A few 

 examples of this sort have been pointed out, especially in the Alps, Avhere wedge-shaped 

 masses of fossiliferous limestone, of liassic age, have been interlaced among the strata of 

 gneiss. Indeed, strata of eocene tertiary have been converted into crystalline gneiss, mica 

 schist, and even into granite beds. In our country not many analogous cases have been 

 pointed out. We present one, which fell under our notice in the town of Derby, on the 

 east shore of lake Memphremagog. The section in Fig. 19 will give an idea of this 

 case as we understand it. Here, as we ascend a hill of moderate elevation, the strata 



