930 



SCIENCE 



[N. S. Vol. XXXI. Xo. 807 



or 250 metei-s along its innei* border, and 

 of from 50 to 120 meters near the coast, 

 where the sea has developed a fully mature 

 line of cliffs which truncate all the sea- 

 board hills in even alignment. The texture 

 of dissection is rather coarse. In conse- 

 quence of a slight and recent elevation, 



mediately infer the total initial structure 

 and form of the district concerned ; second, 

 that it proceeds, tacitly implj-ing the action 

 of normal and of marine processes of ei'o- 

 sion, to state the stage that each of these 

 processes has reached in the regular prog- 

 ress of its work : and third, that it adds in 



Fig. 2. Diagram of the Late Mature Coastal Plain. South of Aucona. Italy; looking West. 



increasing from zero at the coast to 10 or 

 20 metei-s at the inland border of the dis- 

 trict, the larger consequent streams have 

 excavated mature flood plains below the 

 remnant terraces of their earlier valley 

 floors; and during about the same recent 

 period the sea has withdrawn from the 

 maturely aligned cli&s of its former attack 

 and prograded a strand-plain fi'om 200 to 

 300 meters in breadth, which at the river 

 mouths is broadened in faintly convex 

 deltas of about double this measure. Hence 

 it seems as if the recently revived rivei-s 

 had rapidly washed so much waste to the 

 sea, that the waves could not immediately 

 dispose of all of it, and therefore deposited 

 a part of it along the shore, thus pro- 

 grading the strand plain. These features 

 are graphically summarized in Fig. 2. an 

 imagined bird's-eye view, looking north- 

 west. 



The essentials of the above description 

 are, first, that it begins with a general 

 statement from which the reader may un- 



closing a brief account of the result of a 

 slight interruption of the first cycle of 

 erosion due to a slanting uplift of small 

 amoiuit, and with the cautionary words, 

 as if, provisionally suggests the correlated 

 origin of two new features, the terraced 

 valley floors and the prograded strand 

 plain, eoncernhig which our brief excur- 

 sions did not sufi&ee to provide full proof. 

 Let us consider these points in more de- 

 tail. From the term, coastal plain, which 

 is given in the first sentence of the descrip- 

 tion, the initiated reader immediately un- 

 derstands a simple structural mass com- 

 posed of stratified sediments, deposited 

 on a sea floor when the region formerly 

 stood lower than now, and when the sea 

 had its shore on the flanks of the Apennine 

 oldland: but now revealed as a land area, 

 sloping gently seaward, in virtue of a 

 broad uplift without significant deforma- 

 tion. Even if alL this had been explicitly 

 stated, instead of having been only implied 

 in the term, coastal plain, the description 



