STRATIFIED OR SEDIMENTARY ROCKS 295 
be written on a card and placed beside each specimen in the 
museum. 
In localities where no voleanic rocks are available, specimens 
should be obtained from other places. 
XII.—STRATIFIED OR SEDIMENTARY ROCKS. 
SANDSTONE. 
Sandstone is a rock composed of consolidated sand, the 
particles of which are usually quartz. In ordinary sea- 
sand the grains are similar in composition, shape, and 
appearance to those found in Sandstone—z.e., they are 
grains of Quartz. In the original rock, from whose 
disintegration the sand has been derived, the hardest and 
most durable mineral was Quartz-—hence it was able to 
resist the attacks of erosive agencies, whilst the other more 
perishable minerals were carried away in solution or in 
suspension as fine mud. 
Sandstones vary greatly as to their degree of consolida- 
tion, from a mere sand-rock, which is just compact enough 
to stand with a vertical face, to a dense compact gritstone 
sufficiently hard to be used for the grindstones of flour 
mills, The size of the grains also varies, from the most 
minute particles of quartz to grains as large as peas, the 
rock then commencing to pass into a conglomerate. In 
colour, too, a considerable difference is noticeable. This 
arises, not so much from the colour of the Quartz, which is 
commonly white, as from ingredients in the cementing 
material, which holds the grains together. 
For purposes of examination, a number of specimens 
should be obtained. These should range, in texture, from 
fine to coarse, should vary in hardness from soft to 
