MAPS AS GEOGRAPAICAL ILLUSTRATIONS 509 
their control by stream intention. Similar streams entering a 
more active sea would be relatively less competent to carry out 
their intention, and there the deltas would be smooth and 
simple. The best of these deltas is that of the Nogat, a dis- 
tributary of the Vistula, which enters the Haff at its south- 
western end. An elaborate account of the Kurische Haff has 
been written by Berendt (Schr. Phys. Oek. Gesell. Kénigsberg, 
IX, 1868), and a general account of the Kurische Nehrung 
may be found in the essay by Bezzenberger in the Forschun- 
gen zur Deutschen Landes- und Volkskunde (Vol. IIT). 
THE VALLEY OF THE MIDDLE RHINE. 
Sheets 526, 527, 543, 544, 557, 558, 572, 573. 
The long depression which the Rhine follows between the 
Vosges on the west and the Black Forest on the east is 
explained by German geologists as a Graben, produced by the 
downfall of a long block of country between the uplifted old 
mountain masses on either side.t During the depression of the 
block, the Rhine does not appear to have been converted into 
a lake, for borings in the valley floor do not reveal lacustrine 
sediments, but pass through gravels and sands to a consider- 
able depth. It is therefore concluded that the Rhine aggraded 
its course and maintained itself as a river during the time of 
deformation.2, When this is taken in connection with the next 
example, it will be seen that the Rhine in this portion of its 
course must be regarded as a very successful antecedent 
river, neither being laked where its floor was depressed nor 
turned aside where its floor was uplifted. 
The border of the valley is remarkably well defined north 
and south of Heidelburg, and for a considerable distance about 
opposite these points on the west; but only the medial portion 
of this low ground has the features of a river flood plain. On 
either side, and particularly on the west, the valley floor slopes 
*LEpzius: Die Oberrheinische Teifebene und ihre Randgebirge, Forsch. z. deut. 
Landes- u. Volkskunde, I, 1885, 35-91. 
2 PENCK, in Kirchhoff’s Landerkunde des Erdtheils Europa, I, 1887, 232, 318. 
