288 NEW ZEALAND NATURE-?STUDY BOOK 
Rocks. Cuttings showing stratification are within reach of 
most schools; attention should be drawn to these with 
special reference to the definite arrangement of the layers, 
and to the material of which the masses are composed. 
These will invariably be found to consist of particles of 
sand or mud—from which their sedimentary origin may be 
inferred. The presence of fossil shells will serve still 
further to strengthen the inference that they have been 
formed by the agency of water. 
Examination of rocks. An investigation of Rocks 
may be undertaken in three ways. We can investigate their 
macroscopic characters, their microscopic characters, 
and their chemical composition. It is with the first of 
these only that we propose to deal; for necessary as all the 
other methods of examination are in throwing light on the 
structure and origin of rock masses, they are beyond what 
can be undertaken in our primary schools. | 
By macroscopic characters are meant certain external 
characters such as size, form, arrangement and general 
shape of component particles, which can be seen by the 
naked eye, or with the aid of a lens of low power. 
Importance of a fresh fracture. One of the first 
things to be learnt in all examination of Rocks, is the way 
in which weathering conceals their true aspects. The 
nature of some of the operations whereby Rocks are acted 
on by the weather will be explained further. One has 
only to examine a fragment of Basalt showing surface 
weathering to appreciate the difference between the reddish 
earthy exterior and the hard compact core; hence the 
necessity of examining a fresh clean fracture. Still 
weathering under certain circumstances furnishes a 
valuable clue to the nature of certain rocks — the 
weathered surface of a hard crystalline Limestone, for 
instance, will sometimes show many projecting fragments 
of shells and other organisms. 
