POSITIONS OF ANCIENT CONTINENTS 377 
that this wide parallelism of the trend lines over these immense 
tracts indicates a uniform reaction of the latter as units to orogenic 
forces and thereby proves their character of entities in the frame¬ 
work of the earth we have acclaimed these large units as primeval, 
or arch-continents. By comparing their location and general form 
with that of the early Cambric continents, as well as by considering 
the character of the Pre-Cambrian sediments we have shown that 
this tentative inference of the continental character of the large uni¬ 
formly folded areas is well-supported by independent evidence. 
The question of the cause of this world-wide Pre-Cambrian fold¬ 
ing and the interlocking one of the significance of the directions that 
the folding exhibits in different segments of the earth, arise as a 
natural sequence of the study of the parallelism of the trend lines; 
but their solution is not of critical importance for the problem of 
the Pre-Cambrian continents; the recognition of the latter being 
simply based on the grand arrangements of the-trend lines as indi¬ 
cating segmental units of a continental order of magnitude. Never¬ 
theless, the direction of the Pre-Cambrian trend lines is so inti¬ 
mately connected with that of the major axes of extension and the 
distribution of the arch-continents that it seems proper to inquire 
into the probable causes of the world-wide Pre-Cambrian folding 
that are suggested by the trend lines; an inquiry that had to be post¬ 
poned until the folding itself had been traced over the earth and 
its general trend lines recognized. 
The Pre-Cambrian world-wide folding may be due to one or 
several of three groups of causes. It may have originated as (1) 
local folding by terrestrial forces that persisted through immense 
intervals of time and gradually involved the whole earth, (2) simul¬ 
taneous world-wide folding by terrestrial forces, (3) world-wide 
folding by cosmic forces.^ , 
1 These phases of the discussion as well as others are more fully treated than is 
possible here, in the author’s “Existence and Configuration of Pre-Cambrian Continents,” 
in the Bulletin of the New York State Museum, Numbers 239 and 240, pages 65 to 
132, 1922. 
