116 
POPULAR SCIENCE REVIEW. 
habitants of the country at a still more remote period. Among 
the objects of this description found in the overburden above 
the outcrop of the south lode at Eio Tinto was a slab of haema- 
tite about nine inches square and three in thickness, on the 
surface of which were two rows of regularly arranged depressions,, 
each about two inches in diameter. These had evidently been 
made by the action of a small muller of coarse porphyry which 
was found alongside ; doubtless, forming an arrangement by 
which a red pigment was readily obtained by mixing with a 
little water the material ground from the substance of the slab. 
The Roman workings consist of numerous circular shafts, 
sometimes where necessary lined with stone, and seldom more 
than thirty inches in diameter ; these are in connection with 
various tortuous galleries which invariably follow the direction 
of rich branches of ore. By becoming saturated with waters 
holding copper salts in solution, the woodwork of these mines 
has been wonderfully preserved, while its tissue is often more or 
less permeated by metallic copper resulting from the reduction 
of its sulphates by woody fibre. In this way timbers made 
use of for supporting the ground are sometimes in such good 
preservation as to retain marks made upon them sixteen cen- 
turies ago, and letters cut by Roman miners are almost as fresh 
as those carved by a school-boy of the present day. 
The Roman method of drainage was partly by adits, of 
which several of great length are known to exist ; but they also 
employed various mechanical means for the removal of water 
below the level of such outlets. A curious discovery of machinery 
of this class was made some years since in the mine of San 
Domingos where a number of wheels constructed entirely of 
wood, and each 16 feet in diameter, were found placed 
one above another in large cisterns or troughs. Through the 
kindness of Messrs. Mason and Barry I am enabled to give an 
illustration of one of these wheels from a drawing made upon 
the spot. Plate III. represents a plan and elevation of one of 
these remnants of early engineering, as placed in the mines. 
This wheel is constructed entirely of wood, and closely re- 
sembles an ordinary water-wheel with the buckets reversed ; 
only that as the internal and external rings are complete through- 
out, the water, when once taken up, can only escape by the 
openings shown in the sides. In this way water which has en- 
tered the buckets, while that portion of the periphery was passing 
through the well, on being raised to the height of the two 
troughs or launders a, flows into them through these openings 
in the sides of the wheel, and is conveyed by them into another 
trough at a slightly lower level. It is consequently evident 
that by the use of a number of such wheels, one placed higher 
than another, and all turned at the same time by means of 
