ROSS — ON PARALLEL LINES OF ELEVATION. 131 



northerly side of its axial line. It has its great plain, the Sahara, 

 on its northerly side. Taken in connection with the other zone 

 of the table lands to which I have referred, we find an elevated zone 

 extending three quarters of a circumference of the earth, over which 

 one ma}^ travel (from Cape Horn to the Cape of Good Hope) at an 

 average elevation of one mile above the sea-level, though no other 

 plateau on the earth reaches an elevation of one mile. 



Zone No. 2, the Appalachian, has its axial line in the volcanic 

 line apparent along the Northern Andes, the Lesser Antilles, 

 Sicily and vicinity, the volcanic Greek Islands, the Dead Sea 

 region, Pondicherry, and completing the more northerly h?^{ oi 

 the great circle — the highly volcanic belt extending through the 

 entire length of Sumatra. In the remaining part of the (approxi- 

 mately) great circle, we find the volcanic belt of New Zealand and 

 the volcanic Islands of Chatham and Easter. Its apparent develop- 

 ment is chiefly on the northerly side of the more northerly half of 

 its axial line, embracing the eastern half of North America, and the 

 South-west of Europe and Asia. Its highest plateaus reach an 

 elevation of a little more than half a mile in North America and 

 Europe, v^hile in South America and Asia they owe their great 

 elevation chiefly to zone No, 1. 



In North America the part of this zone above the level of the 

 sea consists of two well marked subzones. divided bv the sfreat lin^ 

 of depression extending from the Strait of Bellisle to the Gulf of 

 Mexico. Of these the more northerly is the more extensive and 

 unbroken ; the more southerly having its strata more plicated (see 

 Plate I. Fig. 2), and consisting largely of islands and peninsulas. 

 Similar remarks would characterize the developments of this zone 

 in Europe. and Asia; the more southerly subzone consisting chiefly 

 of the msa^ great peninsulas, Spain and Portugal, Italy, Greece, 

 Asia Minor, Hindostan, Farther India, and also many islands ; — 

 and the more northerly, continental in character, and having for 

 its chief lines of elevation, mountain ranges, such as the Carpathian, 

 the Caucasus and part of the Himalaya. 



Zone No. 3, or the Parimean has its axial line in that very 

 remarkable line of fracture extending across Mexico in a nearly 

 east and west direction, a little south of the city of Mexico, and in 



