14 The Philippine Journal of Science 1923 



Interposed between these two continental platforms we have 

 an intermediate area radically different in its physical features 

 and in its Pleistocene geological history. This area is one of 

 inclosed, troughlike sea basins of great depth, ranging from 

 1,200 to 6,000 meters; elongated islands, mostly presenting 

 very considerable altitudes, their elongation parallel to the 

 troughs; the troughlike basins and the islands arranged in 

 curved lines ; and the islands presenting very conspicuous signs 

 of comparatively recent elevation. This modern elevation in the 

 Philippines in places exceeds 1,500 meters. Most of the inclosed 

 deep sea basins are in the eastern part of the Archipelago ; none 

 of them actually occur within the limits of the area outlined by 

 the Malay Peninsula, Sumatra, Java, and Borneo (see Plate 1). 



MolengraafFs contention that there is a genetic connection 

 between the subsidence of the trough-shaped deep sea basins and 

 the elevation of the adjoining, elongated, paralleling, elevated 

 islands is an entirely logical conclusion. The explanation is a 

 crustal movement in a process of folding or faulting at a certain 

 depth. In other words, we have a large stress area, orogenetic- 

 ally still active and as a result unstable, situated between two 

 stable areas, the latter delimited by the Asiatic and Australian 

 continental shelves. This unstable area extends from Lombok 

 and Celebes to near western New Guinea and northward through 

 most of the Philippine group. This entire stress area has 

 been orogenetically active and hence unstable from the Pleisto- 

 cene, and possibly earlier. It has in consequence been archipe- 

 lagic rather than continental, at least since the beginning of the 

 Pleistocene. There have been intermittent land connections 

 eastward to New Guinea, northward to the Philippines, and 

 apparently southwestward and westward with Java, but probably 

 during the entire Tertiary there was no direct connection across 

 the narrow Macassar Strait between Celebes and Borneo. 



In interpreting probable previous land connections on the basis 

 of the present distribution of plants and animals it is difficult to 

 assign definite values to special groups. We merely know that 

 mammals generally cannot swim across broad separating seas; 

 true fresh-water fishes are also thus limited; batrachians, while 

 adapted to terrestrial life, are primarily adapted to fresh-water 

 marsh conditions, and cannot live in salt water; lizards and 

 snakes are apparently better adapted to fortuitous distribution 

 from one island to another by drift than are the mammals as a 

 group, certainly the larger mammals; birds, bats, and most 

 insects, of course, have the advantage of flight, yet many groups 



