122 PROCEEDINGS OE THE AMHERST MEETING 



position of the sand or gravel of the bar on the marsh or lagoon deposits 

 formed back of the bar, it has usually been assumed that a typical cross-sec- 

 tion of the shore formations at this stage must show peat, silt, or similar ma- 

 terial immediately beneath the retreating bar. Absence of such material might 

 accordingly be interpreted as indicating no retrogression of the bar. The paper 

 shows that frequently marsh and lagoon deposits are not present beneath a 

 retreating bar ; that the presence of such materials in notable quantities should 

 be expected only as an exceptional feature, and that normally they will be 

 present in very small quantities or wholly absent. 



Presented in abstract extemporaneously, with lantern-slide illustration. 



ROLE OF CROSS-WAVES IN THE FORMATION OF TOMBOLOES AND POINTS 



BY EOS WELL H. JOHNSON 



(Abstract) 



A wave meeting an island off a shore at not too great a distance has its 

 course bent because of the gradient of bottom out from the island in every 

 direction. The result is to cause the beach directly back of the island to re- 

 ceive waves at two different opposed angles. These may be called cross-waves. 

 Photographs of such cross-waves with the sandy point which they produced 

 will be shown. This would eventually be built up into a tombolo within cer- 

 tain limiting conditions. 



Theoretically, a shoal with sufficiently sharp gradients on a shore where the 

 prevailing wind does not show too great an angle with the shore should also 

 act in this way and produce a looped bar or a pointed sandy prolongation to 

 leeward and a sandy point of the shore, if not too distant. 



The data are considered worth presenting, as the literature stresses so much 

 the opposite movement from forelands to bay-heads; also as another way in 

 which thick deposits of sand can be formed where not subject to reworking, 

 in the case of a transgressing sea. 



Presented extemporaneously, with lantern-slide illustration. 

 Discussed by Douglas W. Johnson. 



Discussion 



Professor Johnson : The speaker expressed the opinion that the essential 

 factor in forming the cuspate forelands described by Mr. R. H. Johnson was 

 the longshore action of wave-currents causing beach drifting from opposite 

 directions toward a common point, and that the cross-waves were incidental 

 to the process rather than causal. He showed that the same result is produced 

 back of an island without the formation of cross- waves, when shifting winds 

 drive waves in first from one direction, then from another. 



GEOLOGY OF THE COLORADO RIVER IN SOUTHEASTERN UTAH 

 BY C R. LONG WELL, H. D. MISER, R. C. MOORE, AND SIDNEY PAIGE 



(Abstract) 



Geologists of the U. S. Geological Survey, working along Colorado and San 

 Juan rivers in the summer of 1921, studied many detailed stratigraphic sec- 



