Hooks. 
VI 
Basalt, 
is an intimate and compact mixture of many minerals, 
is a rock without any quartz grains, 
does not differ from the lava now poured out by 
some volcanoes. 
lias abundant vesicles caused by steam while yet molten, 
an examination in the field shows that basalt flowed 
down old valleys as ?t lava stream, 
it charred wood, and baked sandstones and burnt 
coal. 
many cooled and hardened streams of basalt can be 
traced to the mouths of old and extinct craters. 
Limestone, 
is fine grained. 
is a water formed and Aqueous rock, 
will effervesce with acids. 
is made up of the same material as coral, and the 
shells of sea crejitures. 
is often a mass of shells cemented together by a base 
or matrix of shells ground up more finely. 
Wo are now in a position to utilize tho facts wo 
have learned for the purposes of classifying rocks. It 
is at once apparent that there are two groat classes of 
rocks — the Aqueous and the Igneous. Later cm we 
shall learn that geologists are acquainted with a third 
class of rocks which originally might have been Igneous 
or Aqueous, but at present are so altered from their 
original condition, that they are termed Motamorphic. 
