6 H. H. Howorth — Course of the Rivers of Siberia. 



Changes in Circumpolar Lands, I collected evidence of this fact, 

 which is now an elementary postulate in physical geography. 



That this rise has gone on for a long time is undoubted. It is 

 equally undoubted that it has not gone on always, since we can 

 measure the ultimate limit of the movement by the shells and other 

 debris of the former tide-marks ; the lines of shells, etc., found 

 furthest south being a measure of the former extension southward 

 of the Arctic Sea. What is plain is, that that sea has been shrinking, 

 and is now shrinking very rapidly, and a great deal of what was 

 under water and under ice not long ago is now dry land. This is 

 universally admitted. 



What is not so generally conceded, what in fact seems to have 

 been entirely overlooked, is, that the result towards which this 

 upheaval of the land and this shrinking of the Arctic Sea are tending 

 was, in fact, reached during the Mammoth age, when it seems to be 

 very certain, as I have tried to show in the Geological Magazine, 

 1889, p. 305, that a large part of the Polar basin was occupied by 

 land and not by water, that the level of the northern part of the 

 great Siberian plain was very considerably higher, and that the 

 period of submergence from which Northern Siberia is now escaping 

 is a new feature, which followed upon a period of higher-level of 

 the dry land in the Arctic region in the Mammoth age. 



If the sea-bottom of the Arctic Ocean was sufficiently elevated to 

 be laid bare over a large portion of the area east of Nova Zembla, 

 there can be small doubt that the Western Siberian rivers could not 

 flow in their present beds. The fall of these rivers is proverbially 

 very slight, and it would be a good deal slighter if they had not 

 carved furrows in which to flow, out of the tundras which they 

 thread. So slight is their flow that in places they seem in a doubtful 

 attitude as to whether they should run north or south. A few 

 figures will be the best evidence of this. These figures I owe to 

 my friend Mr. Eavenstein, who tells me they are absolutely and not 

 merely barometrically correct, having been the result of a spirit- 

 levelling operation carried out between 1875 and 1878. They refer 

 to towns situated for the most part near the head-waters of the 

 rivers in question or their feeders. Tobolsk 266 feet, Omsk 

 279 feet, Tomsk 302 feet, Krasnoyarsk 499 feet. The rivers Ob 

 and Yenissei, however, have high banks, and have cut down their 

 beds very deeply, so that we may take it that the real drop of these 

 rivers from their upper reaches is certainly not more but probably 

 considerably less than 250 to 300 feet. 



Now the deepest known soundings in the eastern part of the 

 Arctic Sea show a depth of about 25 fathoms, and inasmuch as 

 recent Arctic shells have been found by Seebohm 500 feet above 

 the present sea-level, this shows that since the Mammoth age the 

 oscillation of level has been over 100 fathoms. An elevation of 

 from 40 to 50 fathoms, however, operating along the Arctic border- 

 land of Asia, would suffice to entirely reverse the drainage of the 

 great rivers, which must in such a case have flowed southwards. 

 This is a very curious induction, and seems inevitably to follow from 



