416 
SILURIA. 
[Chap. XVII. 
the zealous Spanish geologist *, who published two years ago an excellent geo- 
logical map of the Province of Madrid, has shown that the gneiss and other 
crystalline schists and subordinate limestones pierced by granites, and much 
altered, rise to heights exceeding 7000 feet. These are flanked by schists and 
siliceous sandstones, which are classed as Lower Silurian, because they contain 
the Oruziana or Bilobites, a fossil which occurs in rocks of that age in France 
and Britain. 
A suggestion made by Barrande, from an inspection of three imperfect heads 
of the Trilobite Ellipsocephalus, collected by Casiano de Prado in the Montes de 
Toledo, that the ' Primordial Zone ' is also present in the Peninsula, has been 
completely justified by Casiano de Prado himself, who discovered Paradoxides 
and Conocephalus in a band of red limestone in the Province of Leon (see 
Bull. Soc. Geol. Fr. 1860, vol. xvii. p. 516, the fossils being described by de Ver- 
neuil and Barrande). More recently, in 1863, MM. de Verneuil and Louis 
Lartet also discovered a ' Primordial ' Silurian range with the same species of 
Trilobites near Daroca ; they found it also in various parts of the Silurian Sierra 
which extends from Daroca to Moncayo (' Revista Minera,' vol. xiii. p. 479). 
The upper part of the Lower Silurian corresponding to the Caradoc, if not in 
part to the Llandeilo formation, is fully developed in Spain, especially, as M. de 
Verneuil indicates, in the Sierra Morena, the Montes of Toledo, and the Sierras 
of Aragon, near Origuela, Molina de Aragon, etc. 
In crossing the Sierra Morena from Almaden on the north to Cordova on the 
south, de Verneuil recognized an ascending order. The inferior strata consist of 
schists and some intercalated dark limestones, with quartzose sandstones — the 
latter not unlike the British Stiper Stones (see p. 39). These, being the hardest 
and least decomposable portions of the strata, form the summits or peaks of the 
low ridges, and clearly exhibit the strike or range of the masses, which is from 
east 10° north, and west 10° south. The celebrated quicksilver-mines of Alma- 
den occur at the foot of one of the quartzose ridges of this age, as determined by 
Casiano de Prado t, who published in the ' Bulletin' of the Geological Society 
of France (vol. xii. p. 182) a geological map of this tract. The same zealous 
explorer also traced the continuity of Lower Silurian rocks from the Sierra Mo- 
rena into Gallicia, — the range passing through Estremadura and by the Sierras 
of Gata and Fraucia. Most of the mountains which, extending from S. to N., 
form the boundary between Spain and Portugal may thus be considered to be of 
the same age. The Lower Silurian rocks of the Sierra Morena range eastwards 
to the city of Alcarraz, where they subside under the Secondary formations of 
Murcia. 
The long chain of the Sierra Morena, which extends from Alcarraz to Cape 
St. Vincent, is separated from the metamorphic and crystalline coast-range of 
the Mediterranean by a mountainous country composed of Secondary and Ter- 
tiary rocks. The ages of all the rocks in this coast-range, of which the Sierra 
Nevada is so prominent a feature, are still doubtful. One of the mineral cha- 
racteristics of that lofty region is, that it contains immense masses of limestone 
which occasionally are dolomitic, and rise into lofty peaks, unlike any portion of 
the outline in the Silurian and Devonian rocks of the Sierra Morena. It has 
indeed been suggested by M. Pellico, that the southern coast-chain may be of 
* In the summer of 1866 this high-minded, able, veins, but to have impregnated the vertical strata 
and undaunted explorer died at Madrid, the day of quartzose sandstone associated with carbona- 
after his return from the Canary Islands, a victim ceous slates. The occurrence of mercury with 
to his unbounded zeal for the advancement of such rocks is still more remarkable in the Astu- 
geological science. His death is a serious loss to rias, where mines of mercury are worked in coal- 
the progress of Spanish geology. strata. 
t The mercury of Almaden is said not to form 
