Here, Then, Is A Connexion Sufficiently Close Established Between The Phonolites And The Green Slates, Between The Pyroxenic Amygdaloids And

The serpentines containing copper-ores, between volcanic substances and others that are included under the vague name of transition-traps.

All these masses are destitute of quartz like the real trap-porphyries, or volcanic trachytes. This phenomenon is the more remarkable, as the grunsteins which are called primitive almost always contain quartz in Europe. The most general dip of the slates of Piedras Azules, of the grunsteins of Parapara, and of the pyroxenic amygdaloids embedded in strata of grunstein, does not follow the slope of the ground from north to south, but is pretty regular towards the north. The strata incline towards the chain of the coast, as substances which had not been in fusion might be supposed to do. Can we admit that so many alternating rocks, imbedded one in the other, have a common origin? The nature of the phonolites, which are lithoid lavas with a feldspar basis, and the nature of the green slates intermixed with hornblende, oppose this opinion. In this state of things we may choose between two solutions of the problem in question. In one of these solutions the phonolite of the Cerro de Flores is to be regarded as the sole volcanic production of the tract; and we are forced to unite the pyroxenic amygdaloids with the rest of the grunsteins, in one single formation, that which is so common in the transition-mountains of Europe, considered hitherto as not volcanic. In the other solution of the problem, the masses of phonolite, amygdaloid, and grunstein, which are found in the south of the ravine of Piedras Azules, are separated from the grunsteins and serpentine rocks that cover the declivity of the mountains north of the ravine. In the present state of knowledge I find difficulties almost equally great in adopting either of these suppositions; but I have no doubt that, when the real grunsteins (not the hornblende-grunsteins) contained in the gneiss and mica-slates, shall have been more attentively examined in other places; when the basalts (with pyroxene) forming strata in primitive rocks* (* For instance, at Krobsdorf, in Silesia, a stratum of basalt has been recognized in the mica-slate by two celebrated geologists, MM.

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