10 
POPULAR SCIENCE REVIEW. 
patches of green where springs and water drainage have made 
irrigation possible ; on its eastern side is the range just 
described, and on the western side the high ground, 10,000 
to 12,000 feet, of the commencement of the Cordon de Tontal. 
The hills of Gualilan form a loop bending out of and again 
joining the Cordon de Tontal with an intervening space of 
thirty-five or forty miles. 
These limestone hills stand some 300 to 600 feet above the 
level of the detritus, and have an average bearing of nearly 
north and south; the stratification is distinct and regular, 
dipping towards the west at an angle of 46°; the upper edges 
stand out sharply against the sky. Against this limestone 
on the western side, and rising only some sixty or seventy feet 
above the camp, is clay-slate much split up and weathered. 
Both this last and the limestone are in many places cut through 
at right angles by an intrusive, highly siliceous granite ; this 
granite is found up to a height of 300 or 400 feet in the lime- 
stone. 
The beds of limestone vary in thickness from six inches to 
four feet, but may average about three feet ; the strata are 
divided in most instances by very thin layers of crystalline 
carbonate of lime, and at times by sulphate of lime and by a 
fine powder of amorphous silica. Throughout this limestone 
are found cavities, called by the natives cailas (pipes), or ‘ pipe- 
veins/ which pass through and between the strata, as shown in 
the section, fig. 1, Plate I. The direction varies little from that 
of the enclosing limestone, but the dip is far from constant. In 
many places these ‘ pipes * open into large cavities, one of 
which was found to be fifty feet long, and fifteen feet wide at 
its base, rising between the layers of limestone to a height of 
120 feet, with a varying width ; many of the layers have several 
pipe-veins opening into them. The large cavities contain 
decomposed iron pyrites, and quartz carrying gold and silver in 
about the proportion of one to one and a half ounce of the 
former to two ounces of the latter, and on the floors or bottoms 
iron pyrites, zinc-blende, and occasionally galena ; the pipe- 
veins also contain hydrated ferric oxide or gossan, but in less 
proportion, often as much as half the diameter, varying from 
two to fifteen feet, being filled with a compact iron pyrites with 
quartz running through it. The proportion of gold and silver 
in the gossan and pyrites of the pipe-veins is about the same 
as in the deposits in the larger cavities. 
The quantity of zinc-blende increases as the deposits are 
explored in depth, say to fifty-four or fifty-six fathoms; galena 
occurs in small quantities only, and in most instances near 
the granite, with which it is often mixed ; in such cases the 
granite becomes friable and is easily broken, the thin cracks in 
