108 REPORT—1850. 
Notice on the Geological Structure of Spain, to explain an Outline General 
Map of the Peninsula. By M. E. pe ΨΈΚΝΕσΙΙ,. 
Sir Roderick Murchison presented the first sketch of a geological map of the sedi- 
mentary deposits in Spain, communicated to him by M. de Verneuil, who has lately 
made two excursions in the Peninsula, and who, by his own observations, as well as 
through the information given to him by the Spanish geologists, has cleared up the 
. distribution of the principal masses of rocks. ‘The Portuguese portion of the Penin- 
sula is coloured by Mr. D. Sharpe, whose views respecting the geological structure 
of large portions of Portugal have already been published in the Journal of the 
Geological Society. 
On the mere inspection of the map, it is easy to remark that the central part of 
Spain is distinguished by three chains of mountains which constitute the skeleton 
of the country, the Guadarrama, the Montes de Toledo, and the Sierra Morena. 
Having emerged before the secondary period, these ridges formed islands, around 
which were accumulated the Jurassic and the cretaceous deposits. They havé about 
the same direction, and strike W. and by S., E. and by N. 
Primary rocks.—The highest of these, the Guadarrama, is principally composed 
of granite, gneiss and other crystalline schists. Towards the east, in the vicinity of 
Atienza or Siguenza, these primary rocks disappear under the secondary formations, 
whilst to the west they seem to proceed to the frontier of Portugal. The primary 
rocks are not limited to the Guadarrama, but occur in two other and very distant 
parts of Spain. According to the little map of Gallicia by M. Schulz,- Inspector 
General of the Mines, that province is principally composed of granite, gneiss and 
mica-schist occasionally surrounding patches of slate and limestone, in which no 
fossils have yet been found. ‘There is no doubt that these rocks are of great anti- 
quity, situated as they are at the extremity of the paleozoic chain of Cantabria, of 
which they form a sort of expansion. 
Such is not the case with the Sierra Nevada S.E. of Granada, which offers another 
example of a great mass of crystalline schists. The axis of that bold, high, but not 
extensive chain, striking from E. to W., is composed of mica-schist, the age of which 
appears rather doubtful. The abundance of garnets in the mica-schist, the cry- 
stalline structure and magnesian condition of the thick band of limestone which sur- 
rounds the central part, indicate the energy of the metamorphic action which has taken 
place in this part of Spain. 
Paleozoic rocks.—M. de Verneuil paid more attention to the paleozoic rocks than 
to the others, studying their distribution and collecting their organic remains. The 
Sierra Morena is the only tract in which Silurian fossils have been discovered. The 
Silurian rocks are said to constitute the Montes de Toledo (or the Montes Carpen- 
tanos) and the Sierra Morena, but the fossils seem to be restricted to the last chain. 
This range, of moderate height, is composed of slates, psammites, quartzites and 
sandstones, the real order of which can be unravelled only by the study of their 
organic contents, in a country where very violent dislocations have often placed the 
strata in a vertical position. 
Making a section across the chain from Almaden to Cordova, M. de Verneuil 
ascertained, that, proceeding from north to south, the formations are observed to suc- 
ceed each other in an ascending order. The oldest or lowest traces of life are 
trilobites. They occur in black shivery slates, and belong to species very well known 
in the lower Silurian rocks of Brittany and Normandy. The most common, the 
Calymene Tristani, was up to the present time the only known Silurian fossil in Spain. 
It has been found at Santa Cruz de Mudela by M. Paillette, and at Almadenejos, 
near Almaden, by various Spanish geologists. These two places being situated 
about fifty miles from each other, in a direction nearly east to west, mark with some 
precision the true direction of the strata. M. de Verneuil, assisted by M. Eusehio 
Sanchez, Director of the Mines of Almadenejos, discovered also Cheirurus Tournemini, 
Illenus, near to I. Lusitanicus, Sharpe, Ogygia Buchii, Phacops, Bellerophon bilo- 
batus, &c., associated with the Calymene Tristani and C. Arago; all species peculiar 
to the lower Silurian slates of Angers, Vitré, and other places in Brittany. It is 
worthy of notice, that these trilobites, though the lowest in Spain as well as in France, 
are not the earliest in the order of creation ; they correspond only to the second fos- 
