REPORT OF BOARD OF CONSULTING ENGINEERS, PANAMA CANAL. vitreous debris are also present. The cement is a vitreous product containing in places bodies which are difficult to determine, visible under feeble magnifying power, and which I consider as crystallites of large size. It is really an intimate mixture of a predominating amorphous matter and of fine crystalline particles, resulting from the partial devitrification of the amorphous matter. The rock is tuff. It is interesting to compare with these contemporaneous elements the veined rock behind kilometer 54.41. It is, according to Mr. Termier, a black augitic andesite, with very fine grains, holocrystalline, semiophitic, resembling certain diabases. The diagnosis is as follows: Small tablets of anorthite, sometimes arranged in a vague stream-like texture, cemented by shapeless crystals of augite or by a brownish isotropic matter, which seems to come from the decomposition of the augite. Magnetite is very abundant. The rock is, as I have said, almost identical with that which forms the Cerro Culebra and whose diagnosis is as follows: Augitic andesite.-Disarranged small tablets of anorthite, sometimes zoned and thus retrograding toward the bytownite. In the interstices are grains and pockets of augite and much brownish glass partly devitrified. Consolidation seems to have taken place very rapidly. Many small grains of magnetite are present. Only one of the veins piercing the lignitiferous system vertically has been examined. But there are many others, notably on the Pacific slope the large dikes of Paraiso and that of Pedro Miguel. It is not certain, and not even probable, that all these dikes have the same composition; and if they have (like the Cerro Culebra) given passage to the rocky eruption of the cerros we can not wonder that the latter, though belonging with certainty to the same geologic series, have not everywhere the same composition. Thus a specimen brought over by Mr. Zilrcher, and coming from an upper layer of Miocene sandstone in the upper valley of the Chilibre, gave the following diagnosis: Micaceous andesite.-Large crystals of andesine, sometimes a little zoned; crystals of augite, and black mica (the latter much altered). Mass to a great extent vitreous, in which are isolated microlites of andesine. and others of black mica, the latter badly formed and partly decomposed. This rock has a far different composition from that of Cerro Culebra. It is certainly much less basic. Section of the Pacific slope-Trachytic tus.-The last section of the canal, that of the Pacific slope, needs much less study. There are no more deep cuts. We stated that after having traversed an intermediary region, where the lignitiferous system again appears, cut by large dikes and overlaid by fossiliferous limestone (km. 49), we pass into that extended part of the plain of the Rio Grande which under the alluvial soil seems to be composed entirely of trachytic tuffs. We give here two diagnoses of these tuffs: Cinerite of vitrophyry.-D6bris of brownish or greenish glass with numerous small cavities of an oblong form. Various crystals, feldspar, and augite, partly destroyed. Clayey cement of a light-brown color, with very large patches of a light-green color. This cement is cryptocrystalline. The small cavities are filled with various secondary minerals, among others a cleavable zeolite, feebly birefracting, and with snIall spherolitic tufts of a very dark-green material, probably amphibole. Oinerite of vitrophyry.-Needles of a brownish glass, generally curved; shapeless debris of a violaceous glass; crystals of mica and vitrified feldspar, debris of variable feldspars, oligoclasic albite, or basic feldspars, the whole embedded in an amorphous cement in which very fine crystalline fibers of an indeterminable substance can be distinguished; a great number of small cavities. With these cinerites (rhyolitic tufrs of Mr. Hill) are associated points and knolls of trachyte, as at Cerro Ancon: 1. Trachyte.-Holocrystalline rock which contains only thinly scattered pieces of sanidine with albite and Carlsbad macles. The mass is a confusion of very fine shapeless lamella of an acid feldspar, probably anorthose (occasionally macles); of small needles or small grains of a greenish-yellow nmineral, feebly polychroic, doubly refracting (probably altered mica), and of small awl thinly scattered grains of magnetite. Finally, though the cut of the canal does not meet with them, we call attention to the fact that the plain of Palanquilla, opposite Barbacoas and Frijoles, is composed of the same tuffs with similar trachytic points. We give here the diagnoses of these rocks: Vitrophyrous cinerite, with traces of organisms.-Vitreous debris in various forms, some angular, some perfectly rounded, frequently as curved needles. This glass has a clear light-golden color. It contains here and there gaseous 465A-06 11 161