JOURNAL 
OF THE 
WASHINGTON ACADEMY OF SCIENCES 
Vou. 13 SEPTEMBER 19, 1923 No. 15 
GEOPHYSICS.—Comagmatic regions and the Wegener hypothesis.* 
Henry 8S. WasHinaton, Geophysical Laboratory. 
In the many discussions of Wegener’s hypothesis of sliding conti- 
nents one factor in the problem and a possible test of the correctness 
of his ideas seems to have been somewhat neglected. This is the 
matching of materials at the edges of the pieces in the jig-saw puzzle— 
whether they would fit well together, not in outline but in the character 
of the crustal material, if the parts were slid back into their original 
positions. 
Wegener lays some stress on what he considers to be tectonic 
accordances, such as, along the Atlantic break, those of the Algonkian 
gneiss ranges of Scotland and of Labrador, the supposed continuation 
of the Caledonian fold in Newfoundland, and others. Lake? has 
recently pointed out that these supposed accordances are forced and 
that they can be made to agree only by great and unwarranted dis- 
tortions. Wegener attempts also some stratigraphic and biological 
accordances and alludes to the extension of the plateau basalts of East 
Greenland over Jan Mayen, Iceland, and the Faroe Islands, and to a 
supposed correspondence between the Deccan Traps of India and 
basalts of northern Madagascar. 
The object of the present note is to examine the question of petro- 
graphic accordances, chiefly along both sides of the Atlantic basin, 
in the light of what is known of the bordering comagmatic regions. 
Such a region is, by definition, one of cognate igneous rocks, that 
resemble each other in their general mineral and chemical characters 
and in their petrographic features. In any area these igneous rocks 
form the foundation of the surficial and tectonic features; they form 
1 Received July 23, 1923. 
2P. 8. Lake, Geogr. Journ. 56. 1923. 
339 
