40 THE OPEN BOOK OF NATURE 
selves. Young people, however, are interested in 
fossils even more than in minerals and rocks, and 
the next chapter must contain a short account of 
some fossils that are commonly found. Besides, 
the study of fossils is most important, for these 
relics of past ages are very useful in helping us 
to decide the age of the rocks in which they are 
found. | 
But in regard to the rocks, you must do some 
practical work. Let it be your aim to understand, 
as well as you can, the geology of your own district. 
Cover the ground two or three miles from your 
homes in all directions. Ascertain the nature of 
the rocks and deposits in the area, look for faults, 
erratic boulders, and evidences of ice-action. Observe 
the character of the soil, the dip of strata, and satisfy 
yourselves about past volcanic action. When you 
have accumulated some knowledge of your local 
geology, prepare a map showing the various rocks 
in different colours, and indicate as correctly as you 
can the positions they occupy. Also prepare a 
diagram of a section cut clean through the strata in 
any direction you may think best ; in this way you 
can show the rocks that are below the surface, and 
demonstrate the order of strata. These sectional 
diagrams are not easy to make, but you should do 
your best with them, always being willing to ask 
for information and assistance from friends who 
have more experience. A geological hammer will 
be useful to you on your rambles. Such a hammer 
as is pictured in Fig. 6 can be purchased for about 
a couple of shillings ; you will see it has breaking and 
cutting edges. With the flat end of the head you 
