330 M. E. WILSON 
structural features of the region would be those of the younger 
massif, and all evidence of the former presence of the older batholith 
might be destroyed except for such remnants as happened to remain 
in association with the roof rocks in the geosynclinal belts. 
Mountain-building periods and hence also periods of batholithic 
intrusion occur at long intervals separated by erosion periods and 
the development of peneplains. 
‘The rocks in the vicinity of an intrusive batholithic mass are 
generally highly folded and metamorphosed; hence, if in a given 
area in the vicinity of a batholith flat-lying rocks occur which have 
not been greatly metamorphosed, it may be inferred that they have 
not been intruded by the batholith. : 
Batholiths are composite, and their intrusions continue during 
long intervals of time so that their various parts are only approxi- 
mately of the same age. ; 
Batholithic rocks are lithologically so similar that it is generally 
impossible to distinguish between batholiths of different ages 
except by means of their relationships to other rocks of which the 
age is known. 
Recently A. C. Lawson has contributed an interesting paper 
to the discussion on the “‘Correlation of the pre-Cambrian Rocks 
of the Region of the Great Lakes,” in which he formulates the 
hypothesis that throughout the region extending from the Adiron- 
dacks to northwestern Ontario there were in pre-Cambrian time 
“two and only two periods in which great granitic batholiths were 
developed in the earth’s crust.” On the basis of this hypothesis 
he correlates all the pre-Cambrian rocks occurring in the territory 
to which his hypothesis is applied.t. This hypothesis, if true, would 
undoubtedly greatly simplify the problems of pre-Cambrian 
nomenclature and correlation in the region under discussion; but 
an examination of the hypothesis from either a deductive or an 
inductive standpoint seems to indicate that it is an unwarranted 
assumption. 
The principal fact on which Lawson’s hypothesis of two and 
only two periods of granitic batholithic intrusion was based was 
that at the time the hypothesis was formulated only two periods 
1 University of California Publications, X (1916), 1-10. 
