450 



SCIENCE 



[N. S. Vol. XXVI. No. C6G 



to the organization of his industry; and we 

 may be sure of this, that it will be useless to 

 keep a man on the land, or to bring him back 

 to it, by the inducement of ownership or any 

 other attraction, unless we can educate him to 

 do the best for himself and for the land, in an 

 age which calls for cultivated intelligence and 

 scientific method. — The London Times. 



CURRENT NOTES ON LAND FORMS 



RELATION OF VALLEYS TO JOINTS 



There have been various articles published 

 on the relation of drainage lines to joints, 

 involving a problem of which the gorge of the 

 Minnehaha below its falls may be taken as an 

 example. It is sometimes pointed out that 

 the course of this gorge has been determined 

 by the arrangement of the joints in the hori- 

 zontal rock series through which the gorge has 

 been cut. There can be little question that 

 the process of weathering has taken advan- 

 tage of the . joints in the widening of the 

 gorge, and that its walls exhibit joint faces 

 more or less frequently; but it is also evident 

 that the gorge has been cut backward along 

 the course that the stream had on the drift 

 cover up-stream from the falls; and that the 

 relation of the gorge to the joints is therefore 

 one of accidental superposition, and not of 

 submissive guidance. 



On the other hand, it is often plain that a 

 group of master joints may guide the de- 

 velopment of a new (subsequent) branch 

 stream which grows by headward erosion in 

 the bare walls of a young valley; for in such 

 cases there is no stream falling into the valley 

 from the upland above. Subsequent streams 

 of this origin may be common in some dis- 

 tricts; but if they pass into maturity, they 

 will probably wander on their flood plains so 

 as to depart more or less from the guiding 

 joints beneath the valley floor; and if after- 

 wards rejuvenated by elevation, it is eminently 

 possible that they may stray away from the 

 joints that originally led them. The chance 

 of such straying will increase with the late- 

 ness of the stage at which the first cycle of 

 erosion is interrupted by rejuvenating eleva- 

 tion. 



valleys of southwestern WISCONSIN 



E. C. Harder presents a discussion of part 

 of this problem in a thesis entitled " The 

 joint system in the rocks of southwestern Wis- 

 consin and its relation to the drainage net- 

 work" (Bull. Univ. Wise, no. 138; Science 

 series, iii., 1906, 207-246). He first deter- 

 mined by numerous observations th^ dominant 

 joint directions in a certain part of the Wis- 

 consin driftless area; he next determined, ap- 

 parently from maps, the dominant stream 

 directions of the same district. Then he com- 

 pared these two sets of dominant directions, 

 independently determined, and finds that " the 

 prominent directions of jointing correspond 

 with the prominent drainage directions " (p. 

 232). "Many other forces [than joints] may 

 have been present to modify the result," but 

 their influence is thought to have been small 

 (p. 234). Further investigation is looked to 

 for additional results. 



In all cases of this kind, in which the more 

 or less precise coincidence in the directions of 

 a large number of lines is the chief guide to 

 the conclusion, several critical questions arise. 

 First, what are the limits of error in the de- 

 termination of the measured directions, and 

 what are the limits of discordance in cases 

 that are classed as coincidences? Second, 

 what are the possibilities of coincidence by 

 chance instead of by causal relation? Third, 

 is the conclusion that a causal relation exists 

 between the two sets of lines whose directions 

 coincide, supported by independent evidence 

 that the supposed cause can produce the in- 

 ferred effect? Fourth, are other causes shown 

 to be inoperative? 



Joint directions are determinable easily 

 within small limits of error; but stream direc- 

 tions are much less easily determined, because 

 stream lines are as a rule so irregularly 

 curved. Moreover the curved streams of the 

 mature valleys of driftless southwestern Wis- 

 consin demonstrably depart to-day from their 

 earlier courses to a greater or less extent; and 

 it is therefore not clear whether the present or 

 the earlier courses are to be regarded as joint 

 controlled. Some close analysis, with a quan- 

 titative statement as to the percentage of total 



