472 On the Iron-pyrites Mines of Andalucia. [ Oct., 
i 
just such a plain as it now seems to be, and that the valleys were 
carved out afterwards, and all weariness at the monotony of the 
landscape vanishes in the delight of realizing the idea of a Plain of 
Marine Denudation, not by the aid of maps, sections, and description, 
but the thing itself, the size of nature, yet as clearly shown as in a 
model. 
We may now turn to a few of the mines at work, begmning 
with that of Santa Domingo,* in the province of Alemtejo in Por- 
tugal, not far from the Guadiana and the Spanish frontier. 
The deposit, which is of the usual lenticular shape, but irregular 
in outline, is between 500 and 600 metres long and 70 metres 
across at the widest part, and is split up by several “horses” or 
“yiders” of slate: the ore is uncrystallized iron-pyrites of a dull 
grey colour, intimately mixed witha small percentage, from 23 to 4, 
of copper-pyrites ; the latter sometimes occurs in larger quantity, and 
hard specimens may be picked out containing perhaps 20 per cent. 
of copper. Galena and other minerals are also sparingly present, and 
the joints are thinly coated with carbonate of copper. 
Fic. 2. Sectrion across THE ADIT aT SaAnTA DomINnGo. 
4 2 5 
1. Pyrites. 2. Soft part of the Sahlband. 3. Porcelanized rock. 4. Clay-slate. 
Fig. 2 is a section across the adit. The plane of separation 
between the mineral and the sahlband was most distinctly marked 
and haded to the north at an angle of from 45° to 80°: it was 
marked at some spots by beautifully polished slickenside. The 
sahlband itself consisted of a belt (2), next the ore, of a white, soft, 
quartzose rock, about 2 or 3 metres broad; beyond this is a belt, 
said to be as much as 80 metres broad, of very hard, flinty, por- 
celanized rock (8), white with narrow red stains: this passes out- 
wards into slate rock. Here and there in the outer belt is seen a 
breccia of porcelanized rock and white quartz cemented by oxide of 
* T gladly take this opportunity of acknowledging the courtesy of Mr. Mason, 
the managing partner, who entertained us during our stay. 
