
90. DYNAMICAL GEOLOGY. [Boor III. 
Holland and the Netherlands. The Rhone has deposited an important 
delta in the Mediterranean Sea. The upper reaches of the Adriatic 
Sea are being so rapidly shallowed and filled up by the Po, Adige, 
and other streams, that Ravenna, originally built in a lagoon like 
Venice, is now 4 miles from the sea, and the port of Adria, so well — 
known in ancient times as to have given its name to the Adriatic, is — 
now 14 miles inland, while on other parts of that coast-line the breadth — 
of land gained within the last 1800 years has been as much as 20 © 
miles. Borings for water near Venice to a depth of 572 feet have — 
disclosed a succession of nearly horizontal clays, sands, and lignitiferous — 
beds. Marine shells (Cardiwm, &c.) occur in the sandy layers; the — 
lignites and lignitiferous clays contain land vegetation and terrestrial — 
shells (Succinea, Pupa, Heliz), the whole succession of deposits indica- 
ting an alternation of marine and terrestrial or fresh-water conditions.’ — 
On the opposite side of the Italian peninsula, great additions have © 
been made to the coast-line within the historical period. It is com- — 
puted that the Tuscan rivers lay down as much as 12 million cubic 
yards of sediment every year within the marshes of the Maremma. ~ 
The “ yellow” Tiber, as it was aptly termed by the Romans, owes its — 
colour to the abundance of the sediment which it carries to sea. It — 
has long been adding to the coast-line at its mouth at the rate of — 
from 12 to 13 feet per annum. The ancient harbour of Ostia is now 
consequently more than 3 miles inland. Its ruins are at present. 
being excavated, but every flood of the river leaves a thick deposit — 
of mud on the streets and on the floors of the uncovered houses, — 
Hence it would seem that the Tiber has not only advanced its coast- — 
line, but has raised its bed on the plains by the deposit of alluvium, 
so that it now overflows places which, 2000 years ago, could not have 
been so frequently under water.? In the Black Sea a great delta is — 
rapidly growing at the mouths of the Danube. At the Kilia outlets — 
the water is shallowing so fast that the lines of soundings of 6 feet — 
and 30 feet are advancing into the sea at the rate of between 300 
and 400 feet per annum.* The typical delta of the Nile has a 
seaward border 180 miles in length, the distance from which to the — 
apex of the plain where the river bifurcates is 90 miles. The united 
delta of the Ganges and Brahmaputra (Fig. 130) covers a space of 
between 50,000 and 60,000 square miles, and has been bored through 
to a depth of 481 feet. 
1 Elie de Beaumont, “Lecons de Géologie pratique,” i. p. 323. Geol. Mag. ix. 
(1872), p. 486. 
? See an interesting article by Professor Charles Martins on the Aigues-Mortes, in 
Reveu des Deux Mondes, 1874, p.780. I accompanied the distinguished French geologist 
on the occasion of his visit to Ostia in the spring of 1873, and was much struck with the 
proofs of the rapidity of deposit in favourable situations. In the article just cited some 
valuable information is given regarding the progress of the delta of the Rhone in the 
Mediterranean. Interesting historical information as to geological changes at the ~ 
mouths of the Rhine, Meuse, Elbe, Po, Rhone, and other European rivers, as well as of 
the Nile, will be found in Elie de Beaumont’s “Lecons de Géologie pratique,” yol. i. 
. 253. 
® Hartley, Min. of Proc. Inst. Civ. Engin. xxxvi. p. 216. 
