368 POSITIONS OF ANCIENT CONTINENTS 
earth-crust of fairly uniform composition (Uhlich), a pressure 
and a composition that could be found only in Pre-Cambrian, or 
rather Archean time, and that means a uniform contraction of the 
entire earth-crust, such as could not be invoked for the post-Pro¬ 
terozoic mountain systems. If this view should supply a compe¬ 
tent explanation for the world-wide Archean folding, which sug¬ 
gests the view that in the Proterozoic, and even in Archeozoic, 
time the crust was separated into masses that correspond in posi¬ 
tion if not in area and configuration to the continents of Paleozoic 
and more recent times. 
Eliminating certain younger metamorphic rocks and all of older 
rocks infolded in Paleozoics, the large areas that are then left, 
and lend themselves to our inquiry, are the greater part of North 
America, small regions of South America, eastern Europe, north¬ 
ern and eastern Asia, all inner Africa and western Australia. 
The general facts gleaned from them are complemented by those 
obtained from the unfolded “islands” or blocks. 
The most important of these areas are the so-called continental 
nuclei of North America (Canadian shield), Europe (Baltic 
shield), and Asia (Angara shield). An intended comparison of 
their principal directions of folding presupposes essential contem¬ 
poraneity of the diastrophic revolutions they have undergone. 
This has been established by the correlations carried out by Adams, 
Sederholm, and Willis. It is also to be noted that evidence of a 
like succession of eras and diastrophic events has been found in 
most of the other regions here mentioned as being amenable to our 
inquiry. 
The source for this inquiry is chiefly Edward Suess’ “The Face 
of the Earth,” where there is not only a large store of information 
as to the directions of Pre-Cambrian rock-folding, but where also 
the facts of the general directions of Pre-Cambrian folding in Asia 
and eastern Europe are clearly set forth. Nevertheless the assemb¬ 
ling of the full data on Pre-Cambrian folding, which will be given 
in a later publication, requires laborious search through a widely 
extended literature. 
With these introductory remarks we may briefly survey the pre¬ 
liminary results ('which undoubtedly are still subject to important 
corrections) as to the arrangement of Pre-Cambrian folds. 
