62 
Geology of Sydney. 
minerals. It was formed under water, 1 
and when massive is seen to be arranged 
in layers more or less parallel. 
Now take the piece of granite. Note how very 
different it is from the sandstone, both in texture and 
in the kind of minerals it is composed of. Wo find 
tli at — 
1. Granite contains no rounded grains. 
2. There is no cementing material, the various minerals 
being compressed and knitted together. 
3. If a piece of granite is ground level on one side, or 
if a polished slab is examined, three and often 
four separate and very different minerals can be 
seen as the materials that go to form granite. 
4. These minerals are all angular, are not arranged in 
any definite order, and evidently were originally 
formed just where we see them. 
5. The minerals that form granite are — 
Quartz, which is seen as clear, glassy grains, but too 
hard to be scratched by a steel point. 2 
Felspar, which lies in fairly well defined rectangular, 
grey-white or flesh-colored crystals, and which 
reflect light from their faces. Felspar can be 
scratched by a steel point. 
Mica is seen in lustrous plates which easily split into 
very thin leaves. Mica is in color often silvery- 
white. One species is a deep and shining black, 
but which ehauges to a brass-yellow when altering 
or decomposing. 
1 There are sandstones other than those formed under the sea. Some sandstones 
were laid down on the bed of great inland lakes, or in the waters of an estuary. 
Blown sand and volcanic dust form rocks on dry land resembling ordinary sand- 
stone. 
2 The point of a penknife blade may be made to act as a steel point. 
