56 



►necessary for the existence of a metamorphic region subsidiary to the plutonic and so won- 

 derfully related f o it that, — while, in all unequivocal instances of change in sedimentary 

 rocks from the neighbourhood of a pultonic fluid , the power of the latter has been confin- 

 ed to the narrow limit which we now see (1) to be altered, or, beneath the present base of the 

 rock, has entirely reduced and transmuted it , — in the region in question the power of 

 the plutonic fluid was so much weaker that the original strata of the sedimentary rocks 

 subjected to its influence were Ie ft unobliterated even up to the plane of contact, and yet 

 so much greater that the substance of the entire mass, throughout thousands of yards in 

 thickness, was melted, re-crystallized and arranged in laminae (2). Until these conditions 

 have been defined and illustrated by facts, it is not unreasonable to suspend our judgment, 

 and to believe that the tendency of plutonic rocks ha ving the same ingredients as gneiss 

 to a stratified or zoned structure, and even, where mica is abundant, as in the latter 

 rock, to a laminar arrangement, may hereafter be found to explain the origin of such 

 enormous bedded and laminated crystalline masses, as the Himalayas exhibit, more simply 

 than the theory of metamorphism as at present developed. 



The beds of gneiss are no doubt devoid of that regularity which divisional planes possess, 

 and in this respect resemble strata of deposition, (S) but it appears to me they are not ana- 



(1) Mr. Lyell is not able to adduee an instance of alteration beyond 400 yards from the point of contact , and 

 this he admits to be an extreme case. Elements , vol. 2. p. 403 and 411. 



(2) It is well ascertained that stratified rocks of a limited thickness may be metamorphosed by granitic influence 

 without losing their division into strata, but the difficulty is in conceiving a plutonic action so powerful as to 

 extend to the upper part of a raass of some miles in thickness and reduce it to »a state of seuiifusion" (Ltell's 

 Elements 2d. vol. p. 411) without destroying all vestiges of the original strata in the lower part. The plutonic 

 influence may have been conducted through fissures, but in that case it would be necessary to shew that a system 

 of viens ramifies throughout the Himalayan raass, for instance, almost as complete as those which distribute the 

 blood throughout the body of an animal. If, as seems probable , there are, between the great plutonic tracts of 

 elevation , extensivo tracis suffering depression (such as those covered by the Bay of Bengal or the Indian 

 Ocean generally) their rocks must be exposed to plutonic influence laterally as well as from below, and this 

 would reduce the difficulty. Mr. Ltell says that, »granite may bave been another result of the same action (i. e. 

 that which produced gneiss by semi - fusing sedimentary strata) in a higher state of intensity, by which a thorough 

 fusion has been produced ; and in this manner the passage from granite into gneiss may be explained." Now when 

 in the Himalayas we find miles , and in Scotland great deplhs , of gneiss and its associated rocks , containing 

 frequent beds of granite, it is not easy to conceive how the metamorphic influence in ascending through masses of 

 such thickness, should be so unequal as to rnelt down some portions, while only halfmeltiDg the bulk of the strata. 

 In the lower regions this is quite conceivable, but when we find the same inequality in sections of the mass nenr 

 the summit , that is many miles in some cases above the level whence the action eraanates, the theory seems to halt. 



(3) Ltell's El. 2d. vol. p. 390. The strongest argument in favour of the sedimentary origin of gneiss is that 

 insisted on by Professor Phillips. He says that »in gneiss and mica schist the felspar, quartz and mica are rolled 

 or fragmented masses , shewing clearly that the crystals had been exposed to attrition previous to their 

 deposit" (article Geology in Penny Cyclopaedia vol. XI. p. 139. and Treatise on Geology Ist. vol. p. 112). 

 It is clear that such must be the condition of the ingredients of sedimentary rocks derived from the wasting 

 of granite , and subsequently Consolidated so as to resemble gneiss, as in those ascertained instances where 

 injected granite has been the agent of solidification. But if the fact be universally true with respect to gneiss , 

 it is fatal to the hypothesis of the plutonic origin of that rock in anycase. It is a two edged weapon , howercr, 



