SA OD NEW ZEALAND NATURE-STUDY BOOK 
Notice the ease with which it cleaves, and the direction 
of the cleavage planes, wiz., between the folia. Rocks 
which cleave in this way are said to be fissile, a structure 
which is characteristic of all Schists. Observe the 
glistening Mica on the freshly exposed cleaved surface. 
As the Mica lies in thin plates between the layers, the 
Quartz is not readily seen. Take a thin piece of the rock, 
break it across, and observe the Quartz-layers in the cross 
fracture. 
Test for hardness, and notice that the rock can be 
scratched with the knife-blade. Why is this? What is 
the chief mineral exposed, and hence what mineral is the 
knife cutting or rasping away ? 
Determine the specific gravity, and compare with other 
rocks. 
Compare and contrast with Gneiss, and notice that 1t 
differs from this rock mainly in the thinness of the layers, in 
the more regular arrangement of the minerals, and in its 
fissile structure. 
The Schists in this country are found in the Otago 
province, where they cover large areas ; also along the 
flanks of the Southern Alps in Westland, and in various 
localities in Nelson and Marlborough. They are unknown 
in the North Island. | 
SLATE. 
The term Slate is usually applied to an argillaceous not 
obviously crystalline rock, in which cleavage has been 
well developed, so that the rock splits into thin parallel 
layers. The term, however, is not confined to rocks of 
this class—the well-known maitai formation, which out- 
crops at intervals from the northern portion of Otago to 
the Bay of Islands, is classified as a Slate rock, although 
the fissile structure of the typical Slate is entirely absent. 
