198 SCIENCE-GOS STP. 
Persian opium. At the present time four-fifths of 
the drug used in China is home grown. Whilst 
some is of a treacly consistence, sold in jars, other 
kinds are made into flat cakes, and wrapped in 
white paper. 
(5) European Opium. It has been experimen- 
tally demonstrated that opium, quite as rich in 
morphine as that produced in the East, can be 
cultivated in most European countries, even as far 
north as Sweden, I find it stated that in 1830 a 
surgeon in Edinburgh obtained 56 lbs. of opium 
from an acre of poppies, which he sold at 30s. per 
pound. In France the cultivation is carried on to 
a limited extent, some specimens yielding over 22 
per cent. of morphine, the largest amount of this 
alkaloid noted in any opium. In Germany the 
method yielding the best result is to make the in- 
cisions soon after sunrise, to collect the juice at 
once and evaporate as quickly as possible, the per- 
centage of morphine being higher and the drug 
lighter in colour than when the juice is allowed to 
dry on the capsules. The cultivation of the poppy 
in most European countries will however never be 
carried on to any considerable extent, as the diffi- 
culty of obtaining cheap labour in sufficient quan- 
tity at the exact time, and the uncertainty of the 
weather renders its production too much of a 
speculation. 
To be continued.) 
A HISTORY OF CHALK. 
By Epwarp A. Martin, F.G.S. 
(Continued from page 143). 
The Chalk has contributed, to no slight extent, in 
the formation of the characteristic scenery of a large 
portion of England. On the principle which obtains 
that the harder the stratum, the less the denudation, 
we have the Chalk as one of the few formations which 
have contributed to hill scenery in Great Britain. In 
this connection, it stands almost equally in import- 
ance with the oolites of the Jurassic age, or the 
Carboniferous Limestone. 
The smoothness and regularity of the surface of the 
Chalk Downs is in marked contrast to the angular sur- 
faces and abrupt outcrops of other formations. The 
only differences in the rates of denudation which can 
be identified in the Chalk is shown, broadly, from the 
fact that whereas at the foot of the Downs the rise is 
fairly rapid, yet the tops of the heights are scarped 
back at a greater angle, apparently betokening a less 
power in the Upper Chalk to resist denudation than 
in the Lower, where there is a greater mixture of 
argillaceous impurities. 
The scenery of the Chalk is one of gentle, undula- 
ting, rounded heights ; now rising rapidly, but never 
abruptly, except at its escarpment. Where, as along 
the escarpment of the South Downs, there are 
comparatively extensive tablelands, the surface 
bears little or no relation to the planes 
of stratification, the levelling having evidently 
taken place subsequently to the folding of 
the south of England.  Intersecting the higher 
grounds, are numerous valleys, winding and 
intersecting in all directions, and betokening most 
certainly the action of running water, where now the 
valleys are seldom anything but dry. 
It is noteworthy that these valleys, which when 
filled with running streams, must have left the higher 
grounds above the water in the form of a number of 
jslands, never terminate towards the plain or valleys, 
but always rise to meet the escarpment. In whatever 
manner therefore they have been excavated, their 
drainage must apparently have been towards the sea. 
From this I am inclined to believe that the excavation 
of the valleys is attributable chiefly to marine action 
during the process of its elevation by the sea, being a 
terminating period in that which resulted in the 
marine denudation of the surface of the higher Chalk, 
and its former overlying Tertiaries. The marine 
origin of these valleys is supported by Professor 
Seeley ((Q.J.G.S.), although strongly opposed by 
other eminent geologists. 
In England, from Beer Head, in Devonshire, the 
formation extends in an eastern direction for 200 
miles, its western extension, however, consisting of a 
series of outliers resting upon the greensand, beyond 
which the Chalk is absent. Probably, where we find 
it further west, as in Antrim, this remnant has 
escaped denudation through being covered and 
protected by its mantle of volcanic rock. 
According to Dr. J. Mitchell, the most abundant 
deleterious gas in the Chalk is the carbonic acid, but it 
seems to exist in greater quantities in the lower parts 
of the formation than in the upper. “‘ Fatal effects 
from it were noticed at Epsom, 20oft. down, and in 
Norbury Park, near Dorking, at a depth of 4ooft.” 
When the workmen had sunk through 140 feet of gravel 
and sand on Bexley Heath, and had reached to 30 feet 
in the Chalk, this gas rushed out with such force as to 
extinguish the candles by whose light they had been 
working. Dr. Mitchell states that occasionally 
sulphuretted hydrogen is disengaged from the Chalk, 
probably where a large amount of pyrites is con- 
tained in the Chalk. Sometimes even carburetted 
hydrogen is emitted, and in the making of Thames 
Tunnel there was sometimes sufficient gas to cause 
explosion when coming in contact with lights. 
It is worthy of remark that the broad escarpments 
of the Chalk, and the distances to which they are 
