South African Cretaceous Dinosaurs. 263 



submerged trouglis have also been noted along tbe margin of the 

 Asiatic continent. Two such well-marked channels occur in the ocean 

 at the mouths of the Indus and Ganges. Indeed, the phenomenon 

 would seem to be one common to all the continental shelves. 



Attempts have been made by some to explain the existence of 

 these apparently submerged valleys by assuming that the set of the 

 ocean currents tends to erode the ocean floor and produce depressions 

 which simulate river-valleys in the adjoining seas. This explanation, 

 however, does not seem to have met with much favour ; for it assumes 

 the existence of ocean currents which have not been observed, and 

 also assumes that such currents, if they exist, could erode the 

 ocean floor at very great depths. By others it has been suggested 

 that these continental sea-shelf prolongations of existing valleys are 

 recent land areas which have been submerged. If such depressions 

 were local such an assumption might be made with some certainty, 

 but as they are a common feature all over the earth the questions 

 naturally arise — Where, if they are due to a rise in the sea-level, 

 has the water come from, and how, if they are due to a sinking of the 

 land, comes it about that this has affected all the continental shelves 

 at the same time ? 



The difficulty, however, disappears if we regard these continental 

 shelf depressions as of all ages. The present river-valleys and river- 

 basins are certainly, in the main, of very great age. Indeed, we 

 should treat the seaward prolongations of valleys as proving sub- 

 mergence, just as we treat beds containing marine fossils which are 

 now found at great heights above the sea as proving emergence 

 resulting from the rise of the land. It is not now suggested that 

 elevated marine beds indicate that the sea once stood at that level. 

 The volume of water in the oceans must be regarded as a fixed 

 quantity, the apparent changes in the level of the sea being the 

 result mainly of oscillations of the earth's crust. According to this 

 view these submerged valleys may not be of any particular age. 

 Indeed, some of them may be of Palaeozoic age. The actual ages 

 can only be ascertained by a study of the deposits on their floors 

 and margins, just as the ages of the deposits forming the land surfaces 

 are ascertained by the nature of the fossil remains they contain. 



VIII. — IS^oTE ON South Afeican^ Cretaceous Dinosauks. 

 By E. H. L. S. 



THE result of the Tendaguru expedition to German East Africa has 

 been the discovery by Drs. W. Janensch and E. Hennig of some 

 forty Dinosaurs, I'anging in size from forms larger than Diplodociis to 

 ones as small as a pointer dog ; these finds may be extended since 

 Dr. H. Eeck has proceeded to the locality with the intention of 

 digging for a further year. In a paper by Dr. Hennig on the possible 

 extension of the Dinosaur deposits ^ this author calls attention to the 

 discovery by the late Dr. W. G. Atherstone of Dinosaur remains 

 in the Wood Bed (Lower Cretaceous) of Bushman's River. In his 



^ Sitz. Ges. naturf. Freunde, Berlin, 1912, pp. 493-7. 



