168 
THE TROPICAL AGRICULTURIST. [September 2, 1889* 
dicular instead of the horizontal. But this theory 
of long-continued settlement in quiet water has long 
been abandoned for that of metamorphic changes 
under the influence of heat, pressure and magnetic 
attraction. There may not, indeed, be anything 
wild in the idea, entertained by a writer on the 
gems of Eatnapura, .that electricity operates largely 
on rocks and minerals, in the shape of 
the lightning flashes which our atmosphere 
sends into the earth. Few persons have any 
idea of the large amount of " interstitial water " 
contained in the hardest granitic rocks and 
of the influence of such moisture in inducing 
decomposition and metamorphic action. As Mr. 
Drieberg has mentioned " eruptive" forces, we may 
hope that he will help us to a decision of the 
controversy regarding traces of such action in 
Ceylon, in any period short of the archamn. We 
have frequently heard and read of alleged evidences 
of volcanic action in Ceylon, but we have never seen 
any more closely connected with our rock forma- 
tions than the pumice which has continued to be 
washed on our shores, ever since a year after the 
eruption of Krakatao. 
Then, as to graphitic gneiss, in which plumbago 
takes the place of mica, sometimes so closely re- 
sembling laminae of the latter mineral that the 
natives believe in a transformation which is im- 
possible, Mr. Drieberg will doubtless explain the 
happy peculiarity in our graphite-bearing formations, 
which has given Ceylon almost a monopoly of 
the refractory substance so valuable for crucibles 
in which to melt the precious metals and steel. 
In the rocks of North America there is abundance 
of graphite, but in a diffused condition, particles 
mixed in the rock, which are difficult and expensive 
to separate. What are the conditions and laws 
under which in Ceylon large masses of pure carbon 
are aggregated in sometimes extensive veins ? and is 
the mineral, one of the oldest formations in our 
globe, still in course of growth and aggregation ? 
NOTES ON SOME OF THE GEOLOGICAL 
FORMATIONS IN CEYLON. 
GNEISS. 
By C. Driebekg, b. a., f. h. a. s. 
Gneiss, one of the commonest formations in the 
Island, is a foliated crystalline-granular rock, consist- 
ing of quartz, felspar, and mica. The quartz is white 
or grey : the felspar is of the variety known as ortho- 
clase (a potash felspar) : and the orthoclase is often 
associated with plagioclase felspar, though it is no 
easy matter to distinguish between the two. When 
hornblende replaces the mica we get Hornblende- 
gneiss ; Protogine-gneiss has talc instead of mica, and 
specimens of this variety were shewn me, got out 
of a quarry in Mutwal ; Graphite-gneiss has graphite 
or plumbago instead of mica. It is simply its foliated 
structure which distinguishes gneiss from granite. In 
granite the crystalline particles are intimately mixed, 
while in gneiss, the quartz, felspar, and mica form 
folia, often running into lenticular layers of consider- 
able thickness. 
The question of the origin of gneiss is one that has not 
altogether been set at rest. The most generally ac- 
cepted theory is that all schists are merely metamor- 
phosed aqueous or igneous rocks — metamorphism 
being induced by great heat. In local or contact 
metamorphism the inducing cause is generally an 
eruptive mass, which, intruding in a molten or semi- 
molten state, alters, by its highly heated condition, 
the surrounding rocks. Where the metamorphism is 
regional, the heat produced is to be attributed to 
internal earth movements, which exert a powerful 
shearing aud grinding action. It is probable that 
water plays an important part in most metamorphic 
changes. The interstitial water in rocks would convey 
tuo heat, derived from an eruptive mase or produced 
by earth-movements, in all directions, and the chemi" 
cal action of this water would favour the. re-arrange" 
merit of rock-constituents. 
The metamorphism by mere contact is well seeu 
where an eruptive rock mass lies exposed, resting on 
clay or limestone producing in the former case jas- 
perous stone, aud calcareous silicates such as garnets 
in the latter. The gradual merging of the original rock 
— for instance clay — into the metamorphosed rock is 
most strikingly shown in places in the Matale district, 
where extreme instances of schistosity — resulting in 
seared and puckered foliated rock of very grotesque 
(often vari-coloured) appearance may be observed. 
There exist, however, enormous areas of schistose 
rocks which exhibit no appearance of the gradations 
characteristic of metamorphism by the agencies I have 
indicated above. 
These rocks, always the oldest in the region 
they occur, are the arch:ean sehists,the junction between 
which and the over-lying strata being invariably an 
uncomformability. Some geologists believe that these 
were chemical precipitates of the primeval ocean, 
laid down at a time when the temperature of the 
water was much higher, and the proportion of mineral 
substances much greater than at present — the result 
being what may be termed the chemical sediment of 
a thermal ocean. The weight of evidence, however, 
so far as it goes, seems at present to be against 
this view. — Magazine of the School of Agriculture. 
The Eucalyptus. — When doctors differ, who is 
to decide ? Mr. Robertson recommends the extensive 
planting of the Eucalyptus (blue gum) on the 
Nilgiris, as a profitable investment. The Acting 
Conservator of Forests, in his last report, re- 
marks that the tree, as a forest produce, is a failure. — 
Madras Times, 19th July. 
Dry wood gives a hotter fire, and is more 
economical to burn than green wood, because the 
latter contains more water, and a large part of 
the heat of the fire is wasted in converting it into 
steam, which passes off up the chimney, thus 
carrying the heat into the outer air, where it is 
wasted. — American Cultivator. 
A New Tobacco Co. — The prospectus is published of 
"Laukat Maatschappy" (Limited I, Sumatra, with a 
full capital of £125,000 in £1 shares. The present 
issue is 150,000 shares, of which the vendor takes 
60,000 in part payment of the purchase money, and 
the balance (£15,000) in cash, these payments to in- 
clude all expenses of promotion, &c. The company 
is already a going concern, and calculating the pre- 
sent crop at 2s 3d per lb. it is estimated there will be a 
profit sufficient to pay a dividend of 20 per cent. Next 
season it is proposed to plant on a large scale, when 
an enhanced dividend may be expected. It is very 
probable that the present crop may, however, prove 
more valuable than the estimate of 2s 3d per lb., as 
from the land of the Shanghai Sumatra Tobacco 
Company, which adjoins the estates of the present 
company, tobacco, which contained as much as 51 per 
cent of broken leaf, realised 2s 9d per half kilo. The 
most important fact we may direct attention to, how- 
ever, is that the Deli Maatschappy, whose magnificent 
properties and dividends have been the admiration of 
so many, have consented to act as the representatives 
of the Company in Sumatra and Amsterdam, a fact 
which will ensure the produce being efficiently handled. 
Mr. Wortman, who is interested as one of the 
vendors, and who has had some fifteen years' actual 
experience of tobacco planting in Sumatra, is, we 
observe, one of the directors. It would be super- 
fluous to say much to our readers as to whether 
tobacco planting in Sumatra is a success. The only 
elements needful are that the land should be pro- 
perly selected, and that the seasons be favourable. 
That the first has been done we can be assured, 
as Messrs. Blumenthal and Schoeller, managers of 
the Deli Maatschappy, have reported well on the 
land ; the second, of course, cannot be pronounced 
on.— London and China Express. 
