BY H. I. JENSEN. 511 



same relations hold good. The alkaline rocks specially favour 

 the land-areas and particularly a zone adjoining water-basins. 

 Attention is invited to the distribution of alkaline rocks and of 

 land and sea in Antarctica. 



We must infer from all these facts that the alkaline rocks are 

 situated on the lines of great faults along which differential 

 movements of adjacent earth-segments have proceeded for long 

 periods, producing shore-conditions. 



Situation of Alkaline Rocks with regard to great Fold- 

 Lines. 



If we compare fjg.5 with Neumayr's map (fig. 7) showing the 

 position of the younger folded chains, the fact stands out very 

 clearly that these chains are entirely free from alkaline intrusives. 

 The Rock}'' Mountains with the exception of a small portion of 

 California and Utah, the whole Andes chain, the New Zealand 

 Alps, the fold-range of the New Hebrides and of the Solomon 

 Islands, the Himalayas, the Hindoo-Koosh Mountains, the Alps, 

 and the chain of the West Indies are all avoided by alkaline 

 intrusives. In all those regions which underwent prolonged 

 sedimentation, almost uninterruptedly, through late Palaeozoic 

 and the whole of Mesozoic times and then became folded and 

 elevated in the early Tertiary, the intrusives are calcic granites 

 and gabbros, and the lavas consist of andesites, melaphyres and 

 basalts. Such is the case with most of the areas of the Mediter- 

 ranee Centrale of Neumayr and the Tethys of Suess, and most 

 of the great Pacific area. 



Thus, although granites and gneisses are considered to be 

 typical of continental areas, they are in truth only typical of our 

 present continents, for they occur abundantly in the centres of 

 Mesozoic basins now raised into high mountain-chains; whereas 

 alkaline rocks, which never occur in high folded chains but only 

 in block-faulted regions, may be regarded as typical continental 

 rocks, and those islands of our present seas which contain an 

 abundance of alkaline rocks are in almost all cases relics of more 

 extensive continents disrupted into fragments in the early Tertiary 



