THE PLAN OF THE EARTH AND ITS CAUSES. 383 



The existence of these massive coigns 1 at the three tetrahedral corners 

 has produced one point of divergence in the earth plan from the geo- 

 metrical figure of the tetrahedron. Tbe existence of three such broad 

 massive blocks naturally strengthens the line between them; and, as 

 we have seen, the main divide in the northern hemisphere runs from 

 coign to coign. The tetrahedral edges would naturally be lines of 

 weakness and of movement; but in the northern hemisphere the hori- 

 zontal lines of yielding are deflected southward by the stability of 

 the band supported by the earth's three northern coigns. Hence the 

 great band of disturbances is subtropical, and runs from the Carib- 

 bean to the Mediterranean, across the Persian Gulf and the Malaysian 

 Archipelago. 



In the case of the vertical edges, however, the agreement in position, 

 as well as direction, is exact. Precisely below the three corner blocks 

 there are three lines of instability coinciding with the vertical tetrahedral 

 edges. Below the Canadian coign thereis the line of the Andes (longitude 

 75°), which according to some geologists is still undergoing elevation. 

 Almost 120° east of the Andes, and below the Scandinavian coign, is 

 the Erythrean rift-valley (mean longitude 40°), in which some of the 

 earth movements are unquestionably of very recent date. Again, 

 nearly 120° eastward, and due south of the Manchurian coign, is the 

 recent line of movement represented by the eastern coast of Australia. 



The main mountain system of the world corresponds, then, in 

 direction or position, or in both, with the edges of the tetrahedron. 

 The mountain lines run east and west in the Northern Hemisphere, 

 and run meridionally in the Southern Hemisphere — that is, always 

 parallel to the tetrahedral edges. 



But it will be said there are three great exceptions, for the Ural 

 Mountains, the Appalachians, and the Rocky Mountains are meridional 

 instead of transverse, and tbat they therefore contradict the scheme. 

 The contradiction is only apparent. The existing mountain ranges 

 date from two main periods of mountain-building — the Upper Camozoic 

 and the Upper Paleozoic. The Upper Tertiary system includes the 

 Alps, Andes, Himalaya, Pyrenees, Caucasus, and Atlas, etc. The Urals, 

 Rocky Mountains, and Appalachians belong to the Upper Paleozoic 

 system. Before we can say whether these chains confirm or refute the 

 tetrahedral theory, we must determine the distribution of laud and 

 water at the time when they were made. 



Now, we know that in Upper Paleozoic times one land fauna and 

 flora ranged round the Southern Hemisphere from Australia to India, 

 and thence to the Cape and South America. Instead of there having 

 then been a continuous ocean belt separating triangular points of land, 

 there was then a southern land belt, which was supported by three 



1 The suggestion of the word " coign " for " corner" I owe to Mr. L. Fletcher, to 

 whom I am indebted for much helpful advice. The term is suitable, as it is used for 

 a printer's wedge as well as for the corner stone of a house. 



