Page:A Treatise on Geology, volume 2.djvu/42

 28 the mouths of the Po and the Adige, the Rhone, the Danube, and the Volga, and the numerous streams which enter the Gulf of Bothnia. The rate of augmentation of the deltas in the Mediterranean may be determined by comparing the descriptions of ancient and modern geographers; and in some cases verified by roads, embankments, and other monuments of ancient civilisation. Mr. Lyell has collected evidence of this nature in proof of the considerable increase of land at the mouth of the Rhone, since the era of Roman power, and even during the last thousand years. "Notre Dame des Ports was a harbour in 898, but is now a league from the shore. Psalmodi was an island in 815, and is now two leagues from the sea. Several old lines of towers and sea-marks occur at different distances from the present coast, all indicating the successive retreat of the sea, for each line has in its turn become useless to mariners; which may well be conceived, when we state that the Tower of Tignaux, erected on the shore so late as the year 1737, is already a French mile from it."— (Princip. of Geol., book ii. ch. iv.)

Lower Egypt is the gift of the Nile; and Herodotus estimates the sediments borne by the waters of that river to be so abundant, that if diverted into the Arabian gulf (Red Sea), they would fill it up in 20,000, or even 10,000 years. But the further growth of the great Nilotic delta is checked by a powerful littoral current, which washes the African coast from Gibraltar to Egypt. The accession of new land on the coasts of the Adriatic is perfectly known, since the Augustan days of Rome, and the rate of increase is inferred to have been even augmented during the last 200 years. For by Prony's account (Cuv. Disc, sur les Rev. du Globe), the shore was 9000 or 10,000 metres from Adria in the twelfth century; 18,500 metres in the year 1600; and between 32,000 and 33,000 metres at present; which gives an average yearly increase of breadth of new land of 25 metres from 1200 to 1600, and 70 metres from 1600 to 1800. This augmentation may