33 



ed 3 or only 2 ingredients ; but in by far the greater number certain plates or flakes , 

 as it were , contained a greater proportion of one ingrediënt , and certain portions a 

 greater share of the other , forming thus what by some is called Gneiss. The length of 

 these plates is alwajs disposed parallel to the general direction of the stratum, and the 

 edges are vertical , or nearly so. There were also other stones , in which the component 

 matters were disposed in what may ba called striae ; that is a great proportion of one of 

 its component parts run horizontally through the others in lines parallel to each other , 

 and to the direction of the stratum. Such stones have also been included under the name 

 of gneiss. 



»ïn many of these stones may be occasionally found vertical layers of white fat quartz, 

 running parallel to the stratum, and entirely separating one part of the aggregated matter 

 from the other, without producing the smallest interruption of substance ; nor is the stone 

 more easily broken there than anywhere else. In these stones, when entire, there is no- 

 thing like a schistose, or striated fracture; but in a state of decay, if exposed to the weather 

 in certain situations especially so that ,the rain may lodge on the surface, the stone gradu- 

 ally splits into thin plates like slate, and this seems to happen as readily to pure quartz, 

 or to perfect granites and granitels, as to the gneiss. In other cases again , especially where 

 blocks have been detached, the stone decays concentrically and of course, losing its angles 

 first, becomes a rounded mass (1)." The rocks of what Dr. Hamilton terms the northern 

 intermediate division consist also of granites and gneiss. 



The recent publication in the Journal of the Asiatic Society of Bengal, of Captain Herbert's 

 Report his mineralogical survey of a portion of the Himalayas (2) has shewn that gneiss is 

 the grand constituent of these stupendous mountains, but the gneiss frequently loses its la- 

 minar character and approaches or passes into granite; a species of granitic gneiss is common, 

 which appears very often to form the transition between granite and gneiss. The observa- 

 tions of Captain Herbert appear to me to tend very strongly to the conclusion that the gneiss 

 and granite of the Himalayas were of contemporaneous plutonic origin. The gneissose struc- 

 ture may be simply the consequence of an excess of mica, for in most instances where Captain 

 Herbert notices the occurrence of granite, he adverts to the diminution of the mica. Again, 

 as mica diminishes the laminar structure disappears. Thus at one place the gneiss gradually 

 loses its mica and becomes an unlaminated mixture of quartz and felspar, having the aspect 

 of quartz rock. A rock occurs composed of felspar and hornblende in different proportions 

 apparently very similar to some of the Pulo Vhin varieties; and at one place Captain H. ob- 

 served it passing into gneiss, although in general the transition is abrupt. It occasionaly con- 

 tains mica and even quartz. Greenslate passing into greenstone occurs frequently. The direc- 

 tion of the principal beds into which the gneiss is separated (true strata according to the Wer- 

 nerians and metamorphists,) coincides with that of the mountain zone of greatest elevation, 



(1) Marteh's Eastern India , vol. 2 , p, 187. 



(2) The date of the survey is not given , but Captain Hbrbb&t tras at Altnorah , engaged in it when Bishop 

 Hkbbr visited the mountaios iu 1842. (See Hbbbb's JournalJ. 



22" deel. 1847. E. 



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