Ch. XXXYH.] SCARCITY OF LIME IN" METAMORPHIC ROCKS. 705 



semblages of hypogene rocks occur in different countries; and, sec- 

 ondly, in any one district, the rocks which, pass under the same name 

 are often extremely variable in their component ingredients, or at 

 least in the proportions in which each of these are present. Thus, for 

 example, gneiss and mica-schist, so abundant in the Grampians, are 

 wanting in Cumberland, "Wales, and Cornwall ; in parts of the Swiss 

 and Italian Alps, the gneiss and granite are talcose, and not mica- 

 ceous, as in Scotland ; hornblende prevails in the granite of Scotland 

 • — schorl in that of Cornwall — albite in the plutonic rocks of the Andes 

 — common felspar in those of Europe. In one part of Scotland, the 

 mica-schist is full of garnets ; in another it is wholly devoid of them ; 

 while in South America, according to Mr. Darwin, it is the gneiss, 

 and not the mica-schist, which is most commonly garnetiferous. And 

 not only do the proportional quantities of felspar, quartz, mica, horn- 

 blende, and other minerals, vary in hypogene rocks bearing the same 

 name; but, what is still more important, the ingredients, as we have 

 seen, of the same simple mineral are not always constant (see p. 595, 

 and Table, p. 102). 



The Metamorphic Strata, why less Calcareous than the Fossiliferous. 

 — It has been remarked, that the quantity of calcareous matter in 

 metamorphic strata, or, indeed, in the hypogene formations generally, 

 is far less than in fossiliferous deposits. Thus the crystalline schists 

 of the Eastern and Southern Grampians in Scotland, consisting of 

 gneiss, mica-schist, hornblende-schist, and other rocks, many thou- 

 sands of yards in thickness, contain an exceedingly small proportion 

 of interstratined calcareous beds, although these have been the objects 

 of careful search for economical purposes. Yet limestone is not want- 

 ing even in the Southern Grampians, in Perthshire and Forfarshire, 

 for example, and it is associated sometimes with gneiss, sometimes 

 with mica-schist, and in other places with other members of the meta- 

 morphic series. Where limestone occurs abundantly, as at Carrara, 

 and in parts of the Alps, in connection with hypogene rocks, it usually 

 forms one of the superior members of the crystalline group. The 

 limestones of the Lower Laurentian in Canada, consisting of several 

 distinct bands, one of them containing Eozoon Canadense, and of 

 great thickness (from 700 to 1500 feet), afford a remarkable exception 

 to the general rule. In this instance, however, augite, serpentine, and 

 various other minerals are largely intermixed with the carbonate of 

 lime. 



The general scarcity of carbonate of lime in the plutonic and meta- 

 morphic rocks seems to be the result of some general cause. So long 

 as the hypogene rocks were believed to have originated antecedently 

 to the creation of organic beings, it was easy to impute the absence 

 of lime to the non-existence of those mollusca and zoophytes by which 

 shells and corals are secreted; but when we ascribe the crystalline 

 formations to plutonic action, it is natural to inquire whether this 

 action itself may not tend to expel carbonic acid and lime from the 



