162 
DELTA OP THE PO. 
son he ascribed a certain bituminous, saline, and glu- 
tinous nature to the substances brought do.wn with 
sand by the Rhone. If the number of mineral 
springs charged with carbonate of lime, which fall 
into the Rhone and its feeders in different parts of 
France, be considered, we shall feel no surprise at 
the lapidification of the newly-deposited sediment 
in this delta." 
Delta of the Po. — The Po and the Adige are the 
principal streams which drain, on the one side, a 
great crescent of the Alps, and, on the other, some 
of the loftiest ridges of the Apennines. From the 
northernmost point of the Gulf of Trieste down to 
the south of Ravenna, there is an uninterrupted se- 
ries of recent accessions of land, more than 100 
miles in length, which, within the last 2000 years, 
have increased from two to twenty miles in breadth* 
The town of Adria, which was a seaport in the 
time of Augustus, and in ancient times gave its 
name to the gulf, is now about twenty miles in- 
land. Ravenna was also a seaport, but is now four 
miles from the sea. Spina, a very ancient city, 
originally built on an arm of the Po, on the border 
of the Adriatic, is now more than twelve miles from 
the sea. The deposites consist partly of mud and 
partly of rock, the rock being composed of calcare- 
ous matter, incrusting shells. Olivi found some 
deposites of sand, and others of mud, extending 
half way across the Gulf of Trieste, and states that 
their distribution along the bottom was determined 
by the prevailing current. 
Delta of the Nile. — Some of the ancient poets have 
described Egypt as "the gift of the Nile;" but, as 
Lyell remarks, we have no authentic memorials 
for determining with accuracy the dates of suc- 
cessive additions made to the habitable surface of 
that country. Major Rennell, after exploring the 
country, states that there is no room to doubt that 
* Brocchi, vol. 1, p. 59. 
