Page:The Journal of geology (IA journalofgeology11893univers).pdf/174

decomposed crystals, at first taken from analcime, as well as polyhedral inclusions similar to those of the phonolite of Tingua were obtained. To complete the felicity of the excursion a cutting at the foot of the mountain showed the eruptive rocks to be in part, at least, contemporaneous with Carboniferous strata.

With the data here obtained a paper was prepared and presented to the Geological Society of London (Quart. Jour. 43, 1887) announcing the discovery and general distribution of nepheline and leucite rocks in Brazil, and the general conclusion that the Poços de Caldas eruptive center is volcanic in the most restricted sense of the term, that it is of Carboniferous age, and that here foyaite and phonolite occur as different phases of the same magma.^[1]

The attack on Tingua was now renewed with the expectation that a diligent search would reveal something analogous to the Caldas region. A trip to the top of the peak showed little of interest beyond a dyke of phonolite cutting foyaite at the very summit. An examination of the margins, well shown by the cuttings of an extensive series of railroad and pipe lines (for the water supply of Rio) at the front, a river valley at the back and roads over the ridge at both ends of the peak, showed that the foyaite is limited to the massif and nowhere presents unequivocally the character of dykes. Two cuttings, one a tunnel, through a spur covered with foyaite boulders as if from the outcropping of a dyke, is conclusive on this point, as only gneiss was found in situ. The eruptive rocks are therefore placed like a plaster on the top and slopes of a gneiss ridge in a manner exceedingly suggestive of volcanic conditions. By forcing a way through the dense forest into the crater-like valley of a stream coming from the very heart of the mountain, the long-sought-for evidence of fragmental eruptives and of extensive masses of phonolite in