530 



SCIENCE. 



[N. S. Vol. XIX. No. 483. 



present. Thus, on each of the three lakes 

 there are remains of an old lake surface 

 which rises in a northerly direction about 

 one foot per mile as compared with the 

 modern surface. Lake Geneva in Switzer- 

 land was also studied for the same evi- 

 dences. Sandy deposits apparently mark- 

 ing an old beach were found at Lausanne 

 12 to 14 feet above the present lake level. 

 The paper then discusses briefly the signifi- 

 cance of these facts and of similar facts in 

 other parts of the world. 



The Basin of the Po Jiiver: George L. 



Collie. (Read by title.) 



The paper is the result of field work done 

 on the Po plain in the spring of 1903. The 

 basin of the Po was an arm of the sea dur- 

 ing the Miocene; a portion of the time 

 probably a strait connecting the Adriatic 

 with the Mediterranean, through the pres- 

 ent Col d'Altare. The sea was gradually 

 crowded out by the encroachment of sedi- 

 ments, brought in from the Alps to the 

 north and from the Apennines to the south. 

 Sediments from Alpine sources are coarse ; 

 from Apennine sources, fine. The total 

 area of the basin is 27,000 square miles, of 

 which 16,000 square miles are mountainous 

 and 11,000 square miles belongs to the 

 plain of the Po. Borings in the plain show 

 that it is composed of a series of approxi- 

 mately horizontal sands, clays and marsh 

 deposits, the last including lignitiferous 

 clays. The sands contain marine shells, 

 the clays carry land shells. The whole 

 succession indicates alternation of marine, 

 fresh-water and land conditions. The 

 thickness of the deposits ranges from 572 to 

 695 feet. There is little fine alluvium in 

 the upper Po, the river flowing over coarse 

 deposits; but below the Sisera River allu- 

 vium of a fine type is common. The upper 

 Po is everywhere crowded close to the 

 northern spur of the Apennines, forced' 

 over apparently by the large and heavily 



laden tributaries from the Alps. In times 

 of flood the river carries an immense 

 amount of debris, estimated to be one three- 

 hundredth of its volume. In spite of this 

 heavy load, the river is not aggrading its 

 bed to an appreciable extent. This non- 

 aggradation is due in large measure to the 

 lake system of northern Italy, which drains 

 into the Po and supplies it with four tenths 

 of its water content. During periods of 

 high water in the faU and spring, the sedi- 

 ment-laden streams from the Alps bring 

 their load to the Po and deposit it. The 

 lakes, however, being basins of reception, 

 not only take out the sediments from the 

 drainage, but also store the water and sup- 

 ply it more gradually than do the lakeless 

 streams. Lago di Garda, in time of great 

 rainfall, scarcely changes its level; the 

 small lakes, such as Como or Maggiore, 

 show great changes of level within a few 

 hours, but, on the whole, they all tend to 

 restrain the water. The result is that after 

 the debris-laden streams have deposited 

 their sediments in the Po and temporarily 

 raised its bed, later there comes a volume 

 of comparatively clear water which re- 

 moves the previous accumulations, and an 

 equilibrium is maintained on the whole. 

 The Po is thoroughly diked from Cremona 

 to the marshes of the delta. It is cus- 

 tomary to place the froldo or main dikes 

 at some distance from the river, thus allow- 

 ing the river to overflow the intermediate 

 flood plain or golene for some distance be- 

 fore reaching the dikes. The golene are 

 frequently covered with willows and thick 

 underbrush and the velocity of the current 

 is greatly reduced thereby and there is 

 little active erosion upon the dike itself. 

 The dikes are continually being extended; 

 the extension of dikes accounts in a meas- 

 ure for the rapid extension of the delta in 

 modern times. Between 1200 and 1600 

 A. D. the delta advanced on the average 

 about 70 feet annually; for the last few 



