THE CRYSTALLINE ZONE. 
17 
CHAPTER II. 
THE CRYSTALLINE ZONE. 
It has already been pointed out that the whole area between the 
southern boundary of Sikkim and Lhasa falls into two broad sub-divi- 
sions, an older crystalline and metamorpbic, and a younger, sedi' 
mentary zone. 
The crystalline and metamorphic zone covers the greater part of 
Sikkim and extends eastward through the Chumbi valley into Bhutan. 
The rocks of this zone have been described by various authors, first 
by Sir Joseph Hooker,* subsequently by Mr. Blanford,^ Mr. Mallet ' and 
Mr.Bose,* and recently by Professor E. J. Garwood, whose paper, issued 
as an appendix to Mr. D. W. Freshfield's " Round Kangchenjunga" 
(1903), marks an important advance in our detailed knowledge of 
the geology and physical features of upper Sikkim. Professor 
Garwood has recognised the great difficulty involved in any attempt 
to map separately the component elements of the crystalline complex 
and has therefore merely indicated on the topographical map the 
localities at which the more prominent lithological types occur, wisely 
avoiding any attempt to indicate petrographical boundaries. 
Professor Garwood has shown that the greater part of upper Sikkim 
consists of gneiss and granite, of which all the higher peaks of this part 
of the Himalaya are formed. The gneiss, which is described in detail, 
is referred in great part to a foliated granite, a conclusion with which 
my scanty observations made during a very rapid march along the 
Lachen valley are entirely in accord. In addition to the gneiss, 
metamorphic beds, some of which at least are of sedimentary origin, 
are found along the valley of the Tista and Lachen rivers ; they 
' Himalayan Journals, II (1854). 
i Joiirn. As. Soc. Beng., XL (1871), pt. II, 367— 420 ; XLI (1872), pt. II, 
30—71. 
^ Mem. Geol. Surv. Ind., XI (1874), pt. i. 
* Ree. Geol. Surv. Ind., XXIV (1891), 46, 217. 
) 
C 
