8:2 PHONOLITIC EOCK8. 



difficulty seems to arise from the too intimate and too 

 numerous relations observed in rocks that are thought not 

 to belong to the same family. 



The phonolite (or leucostine compacts of Cordier) is pretty 

 generally regarded by all who have at once examined burn- 

 ing and extinguished volcanos, as a flow of lithoid lava. I 

 found no real basalt or dolerite; but the presence of 

 pyroxene in the amygdaloid of Parapara leaves little doubt 

 of the igneous origin of those spheroidal masses, fissured, 

 and full of cavities. Balls of this amygdaloid are enclosed 

 in the grunsteiu; arid this griinstein alternates on one 

 side with a green slate, on the other with the serpentine 

 of Tucutunemo. Here, then, is a connexion sufficiently 

 close established between the phonolite s and the green 

 slates, between the pyroxenic amygdaloids and the serpen- 

 tines containing copper-ores, between volcanic substances 

 and others that are included under the vogue 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 griinsteins 

 which are called primitive almost always contain quartz in 

 Europe. The most general dip of the slates of Piedras 

 Azules, of the griinsteins of Parapara, and of the pyroxenic 

 amygdaloids embedded in strata of griinstein, 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 al- 

 ternating rocks, imbedded one in the other, have a commor. 

 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 phono- 

 lite 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 griinsteins, 

 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 griinstein, which are found 



