Chap. XVII.] SILURIAN ROCKS IN SPAIN. 415 
undergone much metamorphism, the observer fails to detect here the equivalents 
of the Lower Silurian Rocks * ; but in a few spots the Pyrenees afford traces of 
one member of the system, as characterized by Graptolites, Cardiola interrupta, 
and Orthoceras Bohemicum and 0. gregarium — fossils which have already been 
spoken of as probably representing the base of the Upper Silurian division. In 
the absence then of Lower Silurian rocks, the Pyrenees present a strong contrast 
to the ' Montagne Noire/ near Neffiez, where some of the largest Trilobites of 
that age have been found. 
Palaeozoic Rocks in Spain, Portugal, and Sardinia. — To the south of 
the great chain of the Pyrenees, where several of their formations occur in 
a more or less crystalline state, the Lower Palaeozoic or Silurian rocks have 
much the same development as in Prance. Our acquaintance with the 
order of these rocks in Spain is chiefly due to the researches, during the 
last fifteen years, of my colleague de Verneuil and his friend Ed. Col- 
lomb ; for, whilst it is true that Spanish and French geologists and mine- 
ralogists of ability, such as Ezquerra del Bayo, Casiano de Prado, Schultz, 
Paillette, Amalio Maestre, and others, had made themselves well acquainted 
with the physical and lithological features of many tracts in which the older 
rocks prevail, and that the eminent French mining engineer, Le Play, had 
published a sketch of the mineral structure of the Sierra Morena, it was 
only by a personal examination of the imbedded fossils of the strata in each 
chain that the relative age of the rocks was at length fixed and correct 
comparisons established f. 
A glance at any good map shows that the Peninsula is marked by domi- 
nant chains of mountains more or less parallel, trending from west-south- 
west to east-north- east, and separated from each other chiefly by enormous 
basins of Tertiary age, which, though at much lower levels, are still at 
considerable heights above the sea, and constitute, on the whole, what 
Humboldt has termed a great plateau J. 
Let us first say a few words on the chief central ridge of the kingdom, the 
Guadarama, which passes to the north of Madrid. The late Casiano de Prado, 
* Bull. Soc. G-dol. Fr. ser. 2. vol. i. p. 137. province, and ia completing a beautiful map of 
t This observation has reference solely to the the Asturias. The tracing of Silurian rocks into 
order and classification of the stratified rocks ; for, the Toledo Mountains is due to the zealous re- 
in reference to mineralogy and other departments searches of the late Casiano de Prado, to whom 
of geological science, a vast number of works and we also owe the proofs that the quicksilver-mines 
memoirs have been written during the last century, of Almaden are in Lower Silurian rocks. Many 
by native and foreign authors. See de Verneuil and of the fossils (chiefly Devonian) from the North of 
Collomb, Coup d'ceil sur la Constitution Ge"olo- Spain were first found by M. Paillette, whose de- 
gique de quelques Provinces de l'Espagne, Ap- scription of the rocks of that age is given in the 
pendice Bibliographique, Bull. Soc. Geol. Fr. 2nd Bull. Soc. Gr6ol. France, vol. ii. p. 439. A sketch 
ser. vol. x. p. 138, where a very copious list of au- of ageological map of Spain was also published by 
thors is given, comprising upwards of 160 publica- M. Ezquerra del Bayo in Leonhard und Bronn's 
tions in the last hundred years. At the Meeting N". Jahrbuch, 1851. In several of his excursions M. 
of the British Association for the Advancement of de Verneuil was accompanied by M. Collomb, who 
Science in 1850, I presented, on the part of M. de has likewise given a sketch of the general views 
Verneuil, his remarkable work, the first geolo- they then acquired of the structure of the Penin- 
gical map of the whole Peninsula, accompanied sula in the Bibliotheque Universelle de Geneve, 
by a short notice. Since that time my colleague Even whilst I write M. de Verneuil is again in 
has often revisited Spain, and in 1864 published Spain preparing a new edition of his Map (April 
with M. Collomb a geological map of the Penin- 5, 1867). 
sula. The high antiquity of the crystalline rocks I The mean altitude of the Plateau of Old Cas- 
of G-allicia is affirmed on the authority of M. tile, for example, is from 2150 to 2200 English feet, 
Schultz, who has made a geological map of that and that of New Castile about 300 feet less. 
