Mediterranean Basin and Submerged River-Valleys 
itself is here of considerable breadth, varying from 25 to 50 miles in the Gulf of Lyons, and limited 
by the 100-fathom contour. 
3. Submerged River-Valleys in the Gulf of Genoa.—The remarkable series of submerged valleys 
continuous with the streams descending from the Apennines into the Gulf of Genoa were determined by 
the late Professor Issel, of the University of Genoa, and are of peculiar interest from their number, and 
from the light they throw upon the geological age of these submarine channels. These were described 
by Issel as far back as 1887, but have scarcely received the attention they deserved except perhaps in his 
own country.! 
The soundings upon which the determination of the submerged valleys depend were carried out by 
Captain J. B. Magnaghi in the ship Washington, of the Royal Italian Navy, and were laid down on 
charts which enabled Professor Issel to trace the isobathic contours ; thus it was found that the sinuosities 
became especially well defined along the contour af 200 métres (about 110 fathoms) which marks the 
edge of the Continental Shelf at a distance of about 7 miles from the coast, and were always directed 
towards the coast itself. The following are the names of the streams entering the sea along the coast ; 
the channels of which are actually, or inferentially, continuous with those under the sea, and can be 
distinctly followed to a depth of goo métres, viz., the Bassagno, Polcevera, Giuliano, Aquila, Merula, 
Arma, and the Roja.” 
The valleys which descend through a brief but steep course from the Apennines are eroded through 
strata of successive geological ages in an ascending series as we approach the coast ; and from the fact 
that the channel of the Roja is eroded through Eocene, Miocene, and Pliocene formations, and is 
continued under the bed of the sea, it becomes clear that it is more recent than the newest of these 
formations ; thus establishing the view of the Pleistocene age of the erosion. Issel was able to carry out 
the soundings as far as the goo-métre contour (nearly 3000 feet), indicating an addition of this amount to 
the height of the Alpine region. But this is only a minimum ; as the channels of the rivers might have 
been followed to a greater depth than goo-métre soundings had they been entered on the charts; but 
apparently they were discontinued at this depth.® 
4. The Nile.—It is much to be regretted that the solid channel of the Nile valley cannot be traced 
under the Mediterranean, owing to the enormous amount of sediment which, from year to year, has been 
carried down from the Abyssinian highlands and deposited in the Delta, and beyond in the basin of the 
sea. That there does exist a continuous channel eroded through the Tertiary or still older strata under the 
bed of the Mediterranean, and now covered by its waters, there can be no question. During the great 
Pliocene uplift the solid channel must have undergone similar vicissitudes to those of the submerged river- 
valleys off the northern shores of the Mediterranean, when the river poured its waters into the most 
eastern of the three large lakes into which the sea was then divided. 
On the occurrence of the subsequent Post-Glacial submergence, the conditions were entirely changed; 
and the turgid waters deposited the mud, filling up the channels and ultimately constituting the Delta 
from before the time of the Pharaohs down to the present day. The history of the formation of the 
valley of the Nile is clearly written in the position of the geological formations of Egypt; and on a 
former occasion I have endeavoured to reproduce it in accordance with the evidence these formations 
afford, together with the changes which the Mediterranean has undergone in past Tertiary times." 
1 Issel, Comptes rendus des sciences, Nos. 24th and 31st January 1887; also in his work I/ Terremoto ael 1887 in Liguria, and again in 
Liguria geologia e prehistorica (2 vols., Genoa, 1892). 
2 Owing to the small scale of the Admiralty Charts (No. 2158) I was unable to confirm Professor Issel’s observations by personal detail ; but 
there can be no question regarding their accuracy. 
3 The subject is more fully discussed in the Zrans. Vict. Inst. vol. xxxii. p. 148. In the discussion which followed the reading of my paper, 
Mr. Henry Benest gave some interesting details regarding several submerged river-valleys of the Atlantic, and of the “Swatch off no ground” off 
the mouth of the Ganges. 
4 “Sketch of the Geological History of Egypt and of the Nile Valley,” Trans. Vict. Inst. vol. xxiv. 
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