410 
Phosphorite in Estremadura. 
Of the former, the few which we either visited, or could ohtain infor- 
mation concerning, seemed to consist of granite, which would appear to 
have forced its way through the midst of the slates in several places, 
but not, as represented in the map of the French geologist, Le Play,* to 
constitute a continuous stratum over the country in which it at intervals 
is seen protruding. 
Thus granite forms the hill on which the old town of Truxillo is built, 
and extends for about a league into the plain on the road towards Lo- 
grosan, where it disappears under slates. The latter continue as far as 
a village distant about three leagues from Truxillo, which is built on 
granite. 
We again find ourselves on this rock for about a mile, when it gives 
place to slates, which maintain their ground until we approach Logrosan. 
To the south of that village the granite a third time makes its appear- 
ance in a hill which rises to the height of 400 or 500 ft. ; but, with this 
one exception, the whole of the undulating surface of country which 
occurs round the town, aad from thence to the Monastery of Guadalupe, 
consists either of clay-slate or of quartzite. 
1^ 
6^ 
Section from Truxillo to Logrosan 7 Spanish leagues. 
The granite is often so much acted upon by the weather, as to be 
separated into blocks, heaped one above the other, like the walls of some 
rude building of Cyclopean architecture ; and to such an extent has the 
decomposition proceeded, that we are at first tempted to imagine that the 
blocks must have been transported from a distance, until reminded by 
their local occurrence, and their being piled up, so as to form consider- 
able hills, that they are still in situ. 
To the presence of the beds of quartz just before noticed may perhaps 
be attributed one feature in the physiognomy of the country we are 
describing, which has already been alluded to in this memoir, and which 
indeed has not escaped the attention of other geologists. We mean those 
low ridges of hills, with flattened summits, which here and there inter- 
sect the comparatively level surface of the clay -slate formation. 
These summits are reported by Le Play to be commonly composed of 
quartz; and we are inclined to credit his statement, from what we re- 
marked respecting the character of those above Almaden : nor does it 
seem improbable that the refractory nature of this rock may have enabled 
it to resist the action of those agents of decomposition that have worn 
Annales des Mines, for 1836. 
