Next to these was a clock frame made out of trachyte in the form of a Greek temple.
Walls of grey slate and trachyte, and the yellow stuff is good and plenty.
In the south of the island there are sills and dykes of felsite, quartz-porphyry, rhyolite, trachyte and pitchstone.
The last is in a sienitic rock on the limits of the trachyte.
Not a single specimen of its trachyte has ever been deposited in a European museum.
Some of these are composed of trachyte, others of compact blue basalt with olivine.
This trachyte is greyish white in colour and easily workable, but hardens by exposure.
The prevalence of trachyte shows that the products have cooled under feeble pressure.
The trachyte which once formed the summit of this mountain is now spread in fragments over the plain of Riobamba.
Pumice and trachyte are the most common rocks around this mountain, and these are augitic or porphyroid.