340 JOURNAL OF THE WASHINGTON ACADEMY OF SCIENCES VOL. 13, No. 15 
the main portion of the continental raft, so to speak, which, according 
to Wegener, drifted across the space now occupied by the Atlantic, 
bearing a load of sedimentary deposits the surface of which is corru- 
gated or otherwise roughened by mountain building, warping, erosion, 
and other such dynamical and structural processes. The effects of 
these processes do not extend to the whole depth of the crystalline 
igneous sheet. If, therefore, the crack or line of disjunction ran 
through such a region of chemically and petrographically similar, 
igneous rocks, we should find on either side of the gap areas of corre- 
sponding igneous rocks derived from the basement, even though the 
sedimentary rocks and the fossils and other stratigraphic features might 
not be accordant because of surficial changes that may have taken 
place later than the separation. The following brief discussion is 
based on the second edition of Wegener’s book.? Because of the pre- 
liminary character of this paper the various statements and descrip- 
tions must be put very briefly and only the chief petrographic features 
can be given. Nearly all references must be omitted. The reader 
will find most of the data in Iddings’ Igneous Rocks, Vol. II, and in 
Professional Paper No. 99 of the U. S. Geological Survey. 
The beginning of the Atlantic split and sliding is supposed to have 
been in late Cretaceous or early Tertiary time, but it seems reasonable 
to believe that the time element has little bearing on the phase of the 
matter that is now under discussion. We are dealing here with the 
deep-lying igneous basement, as has been said, beneath the relatively 
very thin skin of sedimentary rocks which record the passage of time 
by their content in fossils and their very shallow movements. Beneath 
these the basal masses of igneous material, whether solidified or as 
liquid ‘‘magma reservoirs,”’ must persist in their general characters 
during and in spite of the epidermal movements above them, the sense 
of which is up and down or radial for the most part. It may be sup- 
posed that the crystalline part of the ‘‘crust’’ which we shall here con- 
sider may, at a rough estimate, extend to about 20 miles beneath the 
surface, possibly rather more according to some estimates.‘ 
In considering the Atlantic split let us begin at the northern end, 
where it is narrowest. Here, according to Wegener’s maps, the north- _ 
west coast of Norway was jammed against the southeast coast of 
Greenland, with Iceland squeezed in between the two. We may leave 
out of consideration the pre-Cambrian gneisses and schists, which be- 
long to the Scandinavian shield. Along the Norwegian coast is much 
3 Alfred Wegener, Die Entstehung der Kontinente und Ozeane, Braunschweig, 1920. 
4Cf. R. A. Daly, The earth’s crust and its stability, Am. Journ. Sci. 6: 360-363. 1923. 
