462 



NA TURE 



[February 18, 1909 



uplift of the land. Both Werth and Philippi describe 

 the occurrence of recent shingle and shells at heights 

 up to about one hundred metres ; but they recognise the 

 possibility of these having been carried inland by sea- 

 gulls or sea elephants. There is abundant evidence of 

 recent subsidence ; the eastern district, according to the 

 chart and many beautiful photographs, presents the 

 typical features of a sunken land. 

 " Dr. Werth discusses at length the origin of the 

 valleys and the relations of the. two types of drowned 

 vallevs known as " fjords " and " fjjirds." The dis- 

 tinction between them was established by Penck in 

 1882 ; fiords are complex and usually branched valleys 

 in mountainous districts, and fjards are valleys that 

 are usually parallel to one another, and occur in low- 

 lands. The value of this distinction has been doubted, 

 but Werth thinks it is useful; and he proposes that 

 valleys of the fjiird type should be called " fohrde," 

 after the name given them in southern Denmark, 

 as it has the same root as the Norwegian fjord, the 

 Swedish fjard, the Icelandic fjordur, and the Scottish 

 firth. 



Denudation in Kerguelen, according to Dr. Werth, 

 is due chiefly to glacial action, for the rivers are in- 

 significant; but Philippi points out that the vallevs 

 were pre-Glacial. Consideration of their age necessarily 

 involves that of the lava flows through which they 

 have been cut. In the neighbourhood of the station 

 the eruptions were obviously pre-Glacial ; but the crater 

 of Mount Ross must be much younger than the lava 

 flows of the eastern lowlands.' The only palaeonto- 

 logical evidence of the age of the eruptions is given 

 by" some fragments of the stem of Cupressoxylon ; but 

 as this conifer ranges from the Upper Cretaceous to 

 the Pliocene, its evidence is not very precise, though 

 the Kerguelen species is regarded as pre-Pleistocene. 

 Wind erosion is exceptionally well exhibited, owing 

 to the violence of the storms and the abundance 

 of loose volcanic debris for the sand blast ; the 

 effect of the wind is illustrated by photographs 

 of a carved block of basalt and of some potholes 

 bored by sand erosion on the face of a vertical 

 rock. 



The important contributions of the German expedi- 

 tions to the natural history of Kerguelen show how 

 great are the gaps in our knowledge of that interesting 

 and accessible archipelago, and will, it may be hoped, 

 lead to its fuller investigation. 



Heard Island, where the German Expedition spent 

 seven profitable hours ashore, is 330 miles south- 

 east of Kerguelen, and is even less known. 

 Both islands rise from the same submarine plateau, 

 and the reports by Philippi and Reinisch show that 

 they are composed of similar volcanic rocks, for 

 Heard island consists of trachytes, felspar basalts and 

 limburgites. The rocks look less weathered than 

 those of Kerguelen, but Philippi suggests, from the 

 greater abundance of trachyte, that the lavas belong 

 to the earlier period of the Kerguelen eruptions. 

 Prof. Drygalski describes the geography of Heard 

 Island and the seven glaciers on the northern 

 coast, Meinardus contributes a sketch of its climate 

 based on all existing records, with the gaps filled 

 by interpolation from the observations on the Gauss 

 and at the station at Kerguelen. In view of the 

 many interesting problems connected with Heard 

 Island, Prof. Drygalski recommends it as a suit- 

 able locality for a year's expedition ; and as at the 

 visit of the Challenger there were forty men on the 

 island who were staying there from October to 

 December, an expedition should be easily practicable 

 and profitable. 



J. W. Gregory. 



NO. 2051, VOL. 79] 



IRRIGATION IX EGYPT. 

 Tlie Esiieh Dam. 



THE construction of the dam on the Nile near 

 Esneh, which has recently been completed, the 

 last stone being laid by the Khedive, marks another 

 step in the progress of that country since it has 

 been under British control. Less than thirty years 

 ago Egypt was on the verge of financial ruin, the 

 annual expenses exceeding the income, and there not 

 being sufficient revenue to pay the interest on the 

 national debt. The peasantry were in a miserable 

 and poverty-stricken condition, and constantly 

 harassed bv the continuous calls under the labour 

 conscription, or corvee, for the repairs of the banks 

 or the cleansing of the irrigation canals. This 

 system has now been entirely done away with ; the 

 small farmers are no longer at the mercy of the 

 monev-lender, and are in a prosperous and contented 

 condition. The revenue shows a surplus, and the 

 yield of the crops has been enormously increased. 



The leading factor in this change has been the 

 better and more effective management, and the 

 extension of the irrigation works, on which the agri- 

 culture of Egvpt depends for its existence. 



The cultivated portion of Egypt consists of a 

 narrow strip of land bordering on the Nile, extend- 

 ing southward from the .Mediterranean Sea. Of this 

 the lower, or southern, district consists of the delta 

 of the Nile below Cairo, forming a triangle, the sides 

 of which are about 100 miles in length, with an 

 area of four million acres, the cultivated portion 

 of which covers 25 million acres. At the head of this 

 delta the Nile water is held up by the great 

 barrages of Rosetta and Damietta. .\bove this is 

 Upper Egypt, a tract 500 miles long, lying princi- 

 pally on the west side of the river, and extending 

 nearly to the first cataract above Assouan. The width 

 of the land that is cultivated varies from eight to 

 fourteen miles, the sand of the desert in many 

 places at the upper end reaching close up to the river. 

 The area of the land under cultivation is about 

 25 million acres, which is dependent entirely on 

 irrigation. Rainfall in Egypt may be said to be 

 conspicuous by its absence, the average fall at the 

 northern end being li inches, and above this the 

 country is practically rainless. 



The Nile is one of the longest rivers in the world, 

 its length from the source to the .Mediterranean being 

 more than 3000 miles. Owing to its physical con- 

 ditions, the fact that it has no tributaries for the 

 last 1500 miles of its course, and the great amount 

 of evaporation under the tropical heat of the sun, it 

 presents the peculiar phenomenon that the quantity 

 of water flowing down the river decreases as the 

 lower length of its course is reached. In floods it 

 carries in suspension detritus derived principally from 

 the volcanic plateau in Abyssinia and the swampy 

 regions of the White Nile. The quantity of material 

 thus transported from the middle of .\frica and 

 .\b\'ssinia has been estimated at 62 millions of tons 

 a year, raising the level of the cultivated land in • 

 Egypt at the rate of 3^ inches in a century, and to 

 a depth which in some places extends to 30 feet. 



The Nile being fed from lands having wet and 

 dry seasons, it has a regular rise and fall, the water 

 through Egypt being at its lowest in June and 

 reaching its maximum in October. The reading of 

 the Nilometer at Rodah is watched with the greatest 

 interest, as the prosperity of the country depends 

 on the height of the flood water. The difference 

 between high and low floods varies ^about loj feet, the 

 mean rise varying from 23 feet at Cairo to 26 feet 

 at .\ssouan at the upper end. The discharge of this 



