DAVIS. — OUTLINE OF CAPE COD. 317 



first reached on the pocket beaches, comes to prevail all along the 

 shore ; ability to do the work of transportation is everywhere equal to 

 the work of transportation to be done. 



In the river problem, the number of independent river systems that 

 occupy the originally deformed surface varies with the strength of the 

 initial relief and with the rainfall. A light rainfall and a strong, 

 rapid-growing initial relief of resistant rocks produce many indepen- 

 dent river systems, and a long time must elapse before a general grade 

 is attained. The early stage of this condition is illustrated in the 

 lava-block mountains of southern Oregon, so well described by 

 Russell (4th Ann. Report U. S. Geol. Survey, 435). But a heavy 

 rainfall and a faint, slow-growing initial relief of weak materials may 

 allow the immediate development of a single river system, soon attain- 

 ing grade over the whole ai-ea concerned. So with the sea. Moderate 

 'long-shore action and strong initial irregularity of resistant rocks break 

 up the 'long-shore currents into many systems at first; the grading 

 of the shore line and the union of the many currents can be accom* 

 plished only after a long time of endeavor. But strong 'long-shore 

 action and moderate initial irregularity of weak materials may permit 

 continuous 'long-shore movements for a long distance on well graded 

 beaches almost from the very first. 



Both in valleys and on coasts — in rivers and on shores — the graded 

 condition will be reached sooner on certain stretches than on others ; 

 and just as an alternation of rough rapids and smooth-flowing reaches 

 indicates a youthful stage of river life, so an alternation of ragged head- 

 lands and smooth-beached bars indicates a youthful stage of shore line 

 development. But in time even the more resistant parts will be 

 trimmed off so as to accord with the less resistant, and then down-stream 

 transportation — or 'long-shore movement — is well developed ; the 

 adolescent stage is reached. From this time forward, on a shore as in 

 a river, the grade is normally changed only where and when a change 

 of load calls for readjustment ; the readjustment necessitating an ag- 

 gradation or degradation of the valley floor, or an advance or retreat 

 of the shore line, as the load may increase or decrease. 



It should of course be understood that comparisons of this kind are 

 not formal comparisons in which the condition of one member may be 

 inferred immediately from those of its analogue. The purpose of the 

 comparison is not to compel explanation, but chiefly to borrow illus- 

 tration of the systematic processes of land sculpture from the better 

 known examples of river action, and apply them to the less studied 

 examples of shore action ; less studied certainly in this country, 



