Phosphorite in Estrcmadura. 
409 
selves that our researches might also prove of practical value, 
even if they should terminate merely in setting at rest a question 
which was exciting some interest at the time in quarters connected 
with agriculture. 
Mr. Pusey, the late active President of that Society, entered 
warmly into our views, and through his kind intervention we 
obtained from the Right Hon. the Earl of Aberdeen, her Ma- 
jesty's Secretary for Foreign Affairs, such letters as were calcu- 
lated to afford us the requisite means of exploring this remote 
and little visited province with comparative comfort and security. 
We are also equally bound to acknowledge the unremitting 
kindness and attention shown us during our stay in Spain, by our 
late Minister at the Court of Madrid, Sir Arthur Aston, by the 
Regent, and by the Spanish Government ; indeed, our obligations 
are due to every individual, without exception, to whom we had 
occasion to apply, either for assistance or information, with reference 
to the object of our inquiries. 
The phosphorite rock is correctly stated by Mr. Bowles to be situated 
at a short distance from Logrosan, which is a considerable village about 
seven Spanish leagues to the south-east of the town of Truxillo, in 
Estremadura. 
It lies in that extensive clay-slate formation, which, with occasional 
masses of quartzite, constitutes the fundamental rock over a large portion 
of the country, from the time of our quitting the flat taV)le-land of ter- 
tiary origin, which occupies the greater part of both the Castiles, till we 
descend the south-east escarpment ot the Sierra Morena, and enter upon 
the plain of Andalusia. 
We first met with rocks, wiiich may perhaps be referable to this for- 
mation, near the village of Calzada de Oropesa, south of Talavera de la 
Reyua, and were led to conjecture that a change had taken place in the 
character of the substratum by the appearance of the country itself, 
which had become more rocky, more diversified, and, at the same time, 
somewhat better clothed with wood* than before. 
In the steep ravine through which the Tagus flows, near to the broken 
bridge of Almaraz, the rocks are observed to consist of a dark blue slate, 
and to be disposed in nearly vertical strata. 
On ascending from thence to the Puerto de Miravete, the culminating 
point of this formation, such a bird's-eye view is obtained of the sub- 
jacent country to the south of us, as, by causing its minor inequalities of 
surface to disappear in the distance, is best calculated to convey to us a 
just general notion of its external configuration. 
We perceive extending before us, so far as the eye can reach, a vast 
table-land, comparatively speaking, level ; but on the one hand dotted 
over at intervals with certain isolated and generally conical knolls, and 
on the other intersected by low ridges with flattened summits, rising to 
the height of 300 ft. or 4U0 ft. above the general level of the plain. 
* Covered, however, chiefly by dwarf shrubs, amongst which the Cistus 
ladaniferus predominated. 
