130 EOSS — ON PARALLEL LINES OF ELEVATION. 



ing subzones for *' anticlinals " in the above, the relations of those 

 tOL^each other will be defined. 



Zone No. 1, or the Eocky Mountain system, has its axial line in 

 the volcanic belt extending from the Middle Andes, inclusive, across 

 Central America, along the ^[locky Mountains, Alaska, the Aleutian 

 Island, Kamtschatka, the Kurile Islands, Japan Islands, Loo Choo 

 Islands, Philipine Islands, Palawan, and Borneo. The Islands of 

 Amsterdam and St. Paul, the Kerguelen Islands, the South 

 Sandwich Island and South Georgia, seem to indicate the comple- 

 tion of the more southerly part of the (approximately) great circle, 

 A belt extending ten degrees on each side of this great circle, 

 includes two-thirds of the volcanoes of the earth. 



On the northerly side of the more northerly portion of this axial 

 line, there is by far the greatest and most unbroken elevated zone of 

 the earth's crust, commencing at the plateau of Bolivia, which has a 

 mean elevation of two and one half miles above the sea-level, it 

 extends to Thibet, which has a, mean elevation equal to that of 

 Bolivia. The higher plateaus in each of these immense and nearly 

 antipodal table lands, as also in the intervening table lands of 

 Equador, reach an elevation of three miles ; and the higher 

 mountain ranges adjacent to them, reach an elevation of from five 

 to six miles above the sea-level. This zone of table lands contains 

 all the plateaus on the earth that reach an elevation of two miles ; 

 and all the mountains of the earth that reach an elevation of four 

 miles are found immediately adjacent to these plateaus. 



On the northerly side of the zone of table lands, is found a 

 zone of plains — by far the greatest and most unbroken of the 

 earth — extending from the mouth of the LaPlata to the Caspian 

 Sea, and at an average elevation of about one-tenth of a mile above 

 the sea-level. Their average breadth may be roughly eatiitiated at 

 1000 miles, and that of the table lands at 1500. 



Commencing at the N. W. extremity of the plateau of Thibet, 

 a zone of table lands extends to the Cape of Good Hope — a distance 

 equal to one quarter of the circumference of the earth. It seems 

 primarily to have constituted part of zone No. 7, which I have not 

 yet described, but to owe its present elevation to its connection 

 with zone No. I, to which it is here approximately parallel on the 



