

304 STRUCTURAL AND FIELD GEOLOGY 
over wide areas, and as these ore-bearing rocks are everywhere 
associated with the same kinds of schist, there can be no doubt that 
they are truly stratiform, and indicate a definite geological horizon. 
Crystalline limestones and dolomites interbedded with certain distinctive 
kinds of schist have in like manner often been traced for long distances, 
and when similar calcareous bands accompanied by the same varieties 
of schist are found cropping out at what might appear to be either lower 
or higher horizons, the probabilities are that such successive outcrops 
are simply the result of folding, the same beds coming again and again 
to the surface. 
It is not unlikely that the observer, while traversing a region of 
schistose rocks, may occasionally encounter areas of less highly meta- 
morphosed strata. He may be able to recognise well-marked clastic 
rocks, such as schistose conglomerate, quartz-rock, phyllite, greywacké, 
limestone, etc. Should such be the case, the strata must be carefully 
followed along and across the strike, for the purpose of tracing the 
changes they undergo as the region of more highly metamorphosed rock 
is approached. The successive bands or zones of distinctive schists 
which we may already have traced through this latter region, we may 
now be able to connect with particular beds occurring in the area of 
less altered rocks. Should such be the case, we shall have no reason 
to doubt that the schists are metamorphosed sedimentary strata; and 
should the direction of their foliation coincide with the dip of the 
individual bands, we shall be justified in concluding that the schistose 
structure has been developed along original planes of bedding. This 
is most likely to be the case when isoclinal folds have been closely 
compressed, so that the rocks are either on end or disposed in highly 
inclined positions. When the folds open out, foliation—often following 
planes of cleavage-—must sometimes have coincided with, and sometimes 
have traversed, the original bedding at various angles. Therefore, the 
mere direction of the planes of foliation, when all trace of bedding has 
been obliterated, cannot, in the absence of other evidence, be relied upon 
as revealing original stratification. 
Just as the observer must be on the outlook for every item of evidence 
that seems to indicate the arrangement of metamorphosed strata, and 
to reveal the original character of the beds, so he must endeavour to 
ascertain what relation the eruptive rocks he may encounter bear to the 
schists they traverse. If they are older than the metamorphism, then 
they themselves will have undergone some change, and may be as 
highly crushed and foliated as the schists. If, on the other hand, they 
are of later date, they will not be metamorphosed. Possibly the geologist 
may encounter igneous masses of older date than the metamorphism, 
which, nevertheless, have a normal appearance. When such masses, 
however, are followed for any distance they will doubtless begin to show 
traces of crushing, and eventually pass into schists or gneisses as they 
near the region of extreme metamorphism. 
Both normal and reversed faults may appear among schistose rocks— 
indeed, faults and extensive thrust-planes may almost be expected to 
