102 CHARLES RICHARD VAN HISE 
series is intricately cut by igneous rocks, all of which stop at a definite 
horizon, this is strong evidence that the adjacent rocks free from such 
intrusives are later and probably belong to a different series. 
g. Amount of deformation.—The amount and nature of the 
deformation are of assistance in correlation within limited areas. 
Upon the whole, the older a series the greater and more intricate the 
deformation. The difference in the amount of deformation in the 
pre-Cambrian series wherever there is a somewhat full succession of 
formations is sufficiently great to make this an important factor in 
the classification and correlation of the formation. 
10. Degree of metamorphism.—The amount of metamorphism 
is a factor in correlation. Upon the whole, the older a series the 
more likely it is to be metamorphosed, but this criterion has severe 
limitations, since within comparatively short distances the closeness 
of folding and the quantity of intrusives may greatly vary, and these 
are very important factors in metamorphism. The worker among 
the pre-Cambrian rocks must have a very thorough understanding 
of the principles of metamorphism and the nature of the transforma- 
tions through which rocks go. For, in working out the stratigraphy 
of the pre-Cambrian, if the criterion of the original character is to be 
used, it is necessary to know the rocks which the now greatly meta- 
morphosed varieties represent. 
GENERAL STATEMENT 
In actually working out the succession of formations, series, and 
groups in the different districts of a geological province and in corre- 
lating them, all of the above criteria must be used. It is in judgment 
in appreciating the value of each of these criteria and their combina- 
tions that the skill of the pre-Cambrian stratigraphical geologist 
appears. 
To this time, from my point of view, the only divisions of the pre- 
Cambrian which have been proved to be general, if not world-wide, 
are those of the Archean and the Algonkian. This subject I shall 
not take up in detail, since I have recently discussed it in another 
address." 
tCharles Richard Van Hise, ““The Problems of the Pre-Cambrian,” Bulletin, 
Geological Society of America, Vol. XIX, pp. 1-28. 
