48 SYSTEMS OF LIFE DESTROYED. 



now know of chemical geology ; for water cannot hold in solution silicates enough for the 

 purpose, nor does the order in which the materials are arranged correspond with that in 

 which they would crystallize if they were in solution. No possible reason can be given, 

 for instance, for the alternate layers of quartz and mica, or feldspar, or hornblende, or 

 talc, which occur in the foliated rocks. 



The theory of metamorphism has fewer difficulties. It supposes these rocks originally 

 deposited as sand, clay, pebbles, marl, &c., after consolidation to have been converted 

 again into a plastic state by the permeation of hot water and steam, charged with power- 

 ful chemical re-agents. We know that this agency is sufficient to bring the silicates into 

 a sort of aqueo-igneous plasticity, and that is all that is necessary to produce the imper- 

 fect kind of crystallization which the azoic stratified rocks exhibit. It is not that com- 

 plete crystallization which would result from thorough solution, either aqueous or igneous ; 

 but the original mechanical texture sometimes exhibits itself, and many degrees of crys- 

 tallization are often manifest. 



Some may be inclined to impute the hypozoic, and perhaps in general more highly 

 crystallized foliated rocks, to some other agency than metamorphism. But we often find 

 rocks of the same kind, and often as highly crystallized, so connected with fossiliferous 

 rocks, that we are compelled to regard them as metamorphic, and it seems difficult to 

 conceive that the others have not had the same origin. All the difference between the 

 two classes, is the more complete metamorphism of the hypozoic. We seem compelled, 

 therefore, to admit the metamorphic origin of all the azoic foliated rocks, or to deny it to 

 them all ; and we cannot take the latter ground but in defiance of the plainest facts. 



5. Metamorphism may have obliterated successive systems of life. We know it to have 

 done this in some of the foliated rocks in the schists for instance that overlie, or are 

 interstratified with, fossiliferous rocks. It may have done the same with all the hypozoic, 

 in all of which no certain examples of fossils have yet been found, though some bodies of 

 doubtful nature have been described in them. 



If this conclusion be admitted, it follows that we cannot tell when life first appeared on 

 the globe, because we know not but an indefinite number of organic systems may have 

 been obliterated. This inference, which some eminent geologists have adopted, would be 

 fair, were it not for certain other facts, which we will state in the words of Sir Roderick 

 I. Murchison. " In Bohemia," says he, "as in Great Britian and North America, the 

 lowest zone containing organic remains, is underlaid by very thick buttresses of earlier 

 sedimentary accumulations, whether sandstone, schist, or slate, which, though occasionally 

 not more crystalline than the fossiliferous beds- above them, have yet afforded no sign of 

 former beings." "The hypothesis that all the earliest sediments have been so altered as 

 to have obliterated the traces of any relics of former life which may have been entombed 

 in them, is therefore opposed by examples of enormously thick and raised deposits beneath 

 the lowest fossiliferous rocks, and in which, if animal remains had ever existed, some 

 traces of them would certainly be detected." (Siluria, pp. 20, 21.) 



6. Metamorphism throws light upon the origin of the granitic rocks, such as granite, syenite, 

 and perhaps some varieties of porphyry. The prevailing opinion has been that they consist 

 of melted volcanic matter, thrust into cracks in the overlying strata, and cooled and crys- 

 tallized under great pressure and with extreme slowness. It is found, also, that other 



