Page:A Treatise on Geology, volume 2.djvu/109

 CHAP. VII. Newry pitchstone by Knox (W. Phillips's Mineralogy, the bitumen and water omitted); and in column 4. a granite of 3 parts quartz, 2 parts albite, and 1 part mica.

Pumice, the last term of this siliceous series, is stated by W. Phillips to be composed of

As an example of greystone? lava, Dr. Kennedy's analysis of the compact lava of Calabria may be quoted:—

Basalt, which belongs to almost every geological age, constitutes the last term of this series, in which silica is diminishing continually. It is very irregular in composition, as might be expected from the character of its predominant ingredient, hornblende or augite. The basalt of Hasenberg in Saxony, according to Klaproth, is composed of

That of Staffa, according to Dr. Kennedy,

Interposed Beds.—As before observed, the want of stratification is one of the characters of igneous rocks; yet there are two cases in which they show themselves in stratiform masses, which seem exceptions to the rule.