GEOLOGY. 185 
fact a foliated form of granite, with the constituent minerals arranged 
in layers. Nevertheless, it is generally easy to discriminate at a 
glance between ordinary sedimentary strata, voleanic rocks, whether 
intrusive or eruptive, granitic rocks, and schistose formations includ- 
ing gneiss, and in all sections the occurrence of these different classes 
of rocks must be noted. 
One of the commonest difficulties in ascertaining the bedding of 
rocks is caused by cleavage, which is especially seen in slate. Ifa 
rock is found to be easily fissile, observation will show whether the 
direction of the cleavage is the same as that of the bedding, which it 
is usually easy to recognise, especially on a weathered surface, by the 
occurrence of stratified bands differing in mineral character, in colour, 
or in resistance to the action of atmospheric erosion. The relation 
of cleavage planes to the stratification should be carefully noted, and 
also to the general outline of the country, especially to the direction 
of hill ranges. 
Jointing is another feature of rocks that may occasionally mislead. 
It consists of parallel-joints or cracks, frequently in more than one 
direction, and often rendered conspicuous by weathering, as the rocks 
decompose more readily along the joints than elsewhere, and con- 
spicuous cracks or fissures are produced. The bedding may be 
distinguished by the same features as those already noticed in the 
remarks on cleavage. Jointing often affects hard solid rocks, such as 
sandstones, limestones, basalt and granite. 
Wherever a section is made, specimens of every rock observed 
should be collected and carefully labelled, so that the formations 
exposed in the section may be subsequently identified. Specimens 
should be taken from rocks in place, not from loose fragments, and 
some care is necessary to select portions of the rock that have not 
undergone extensive alteration from exposure. One surface at least 
of every specimen taken should be a clean fracture of apparently 
unaltered rock. By means of the specimens any difficulty in deter- 
mining the name to be applied to a rock can be removed. 
Voleanic rocks and glacial formations receive separate notice. 
With granitic, gneissic, and schistose rocks little can be done except 
to note the direction of any foliation that may exist; to ascertain 
whether the strike and dips are approximately constant; and to 
collect specimens of the different rocks exposed. Where the whole 
area examined consists of gneiss and schist, detailed sections, unless 
made by experienced geologists, are not worth the great amount of 
trouble they involve. 
In case of the rocks being completely concealed hy ice, some 
