328 Proceedings of the Royal Irish Academy. 



Tersely into mountain chains, ■with intervening desert platforms. Its 

 southern extremity is formed by the Himalayan and other ridges ; 

 their general level, from 20,000 to 24.000 feet in altitude, culmi- 

 nating in still loftier peaks, some not far short of 30,000 feet. 

 All the transverse ridges, in a great portion of their length, have 

 an east and west course; while their terminations generally curve 

 northwards. 



The development of High Asia is a vastly complex phenomenon, 

 presumably resulting from disturbances which have been directed 

 along diiierent zones of weakness. The zone in correlation with equa- 

 torial jointing seems to have been the medium through which the 

 transverse ridges and their individual igneous axis were upheaved ; 

 while those referrible to the two principal sections of meridional 

 jointing may have similarly influenced their terminations on both 

 sides of this huge plateau, especially in the region east of it ; where 

 mountain ranges, coast-lines, and off-lying islands all coincide in 

 their strike with the east-of -north meridional jointing. The lofty 

 parallel ridges east of Burmah, in being medio-meridional, are so far 

 in conformity with the last-mentioned features. This abstract will 

 scarcely permit of any reference being made to the equatorial exten- 

 sions from the Pamir through Western Asia, &c. 



Respecting another prominent feature of our continents, it is 

 assumed that the east-of-north and the west-of-north sections of 

 meridional jointing have primarily marked out the sides of the 

 triangle, under which form these great land masses are for the most 

 part presented ; while the base of the triangle is ascribed to equatorial 

 jointing. Eut it is not yet clear why the base of the triangle faces 

 the north, and its apex points to the south. The writer thinks the 

 solution lies in the fact that the greatest elevated land masses 

 characterise the JS^orthern Hemisphere and equatorial regions ; a dis- 

 position which would cause a greater width of elevated land to lie 

 within the basal area of the triangle than at the apex. 



The cjuestion next suggests itself, arising fi'om a consideration of 

 all the phenomena noticed in the memoir, — if the original elevated 

 plateaus have always existed as masses, having an elevation far above 

 the bottom of the great intervening depressions (oceans) — how have 

 they become covered up with oceanic sediments thousands of feet in 

 thickness, and representing successive geological periods ? In this con- 

 nexion it is argued that elevations of rock-masses are of two kinds : — 

 one due to stratial disturbances, which for the most part have been ex- 

 erted horizontally, or approximately so ; and the other to vertical move- 

 ments, extending over wide geographical areas. The author's early 

 attention was called to the latter class of movements by the beautifully 

 developed series of terraces in the Burren of Clare, reaching to the 

 height of nearly 1200 feet. He ascribes tliis particular instance to a 

 slow upheaval of the district above the sea, the sui-face of each terrace 

 representing the bottom of a shore-line — a plane of marine denuda- 

 tion, and an apparent stoppage in the upheaval. The terraces of 



