ABSTRACTS OP PAPERS 



/.) 



the glacial and alluvial deposits which at one time filled the valley of the 

 Mississippi River in this region. 



It may be well to inijuire if all so-called mounds in the Mississippi Valley 

 are not natural topographic forms. 



Presented in abstract from notes. 



Discussed by Messrs. John L. Eieh and A. E. Crook. 



CAN V-SHAPED VALLEYS BE PRODUCED BY REMOVAL OF TALUS? 



BY ALFRED C. LANE 



(Abstract) 



The top of a talus slope accumulating at the foot of a vertical cliff of height 

 (h) describes a convex curve, which, if n (the ratio of increase of volume 

 occupied by a given weight of rock when broken into talus, usually 1.5 to 2) 

 be 1, if s is the slope of repose, usually .6 to .7, and if y/ be measured fi-oui 

 the foot of the cliff, x from the initial face, is a parabola '2lis.c = //=. If n is 

 not 1, the curve is similar, but has the more complex expression, 



(1 — n) sxh— (y/h) J^ (n/ (n — 1)) nat. log (1— (v/ — 1) ij/nh) 



A cross-section of a talus pile is like a jib or lateen sail, pteroid. Scenic 

 curves may be found which seem to have this origin, but they are just the re- 

 verse of the U-shaped curves of many glacial valleys, which can not have been 

 formed by the mere cleaning out of a widened I-shaped canyon (see figure li. 



FiOCKi: 1.- Talus iiroilutcil bu tha Retreat uf the lc> lical (.'tiff AU, alluwintj fur hilrral 



Weatheriitij only 



The slope of the angle of repose (35°) Is taken as .7. CG Is a parabola and r(il<' is 

 the shai>o of cross-section, If the rock is supposed to occupy the same Itiilk in talus as In 

 cliff — that is, ('(;!'' = ACC in = 1). H<JK is the shape of the section. If the rock in talus 

 occupies twice the l)uik Ihal it does in the clilf, B(1E -- 215GA(» = li). 



In real views sliowing somewhat this type of prollle (see American I'-orestry, June, 

 1914, p. ;J9.') ; Twentieth Ann. Kept., U. S. Geological Survey, part v. pi. ixKt the angle 

 at BC Is rounded, as the weathering Is never iiureiy lateral. 



Presented by title in the absence of the aiitlior. 



