A Manual of Elementary Geology or, The Ancient Changes of the Earth and its Inhabitants as Illustrated by Geological Monuments

CHAPTER XXVIII.

Chapter 3165 wordsPublic domain

VOLCANIC ROCKS.

Trap rocks--Name, whence derived--Their igneous origin at first doubted--Their general appearance and character--Volcanic cones and craters, how formed--Mineral composition and texture of volcanic rocks--Varieties of felspar--Hornblende and augite--Isomorphism--Rocks, how to be studied--Basalt, greenstone, trachyte, porphyry, scoria, amygdaloid, lava, tuff--Alphabetical list, and explanation of names and synonyms, of volcanic rocks--Table of the analyses of minerals most abundant in the volcanic and hypogene rocks 366