66 J. B. Woodworth — Post- Glacial 



since the direction of the wind in the desert often changes every 

 hour. 



" On the other hand, I have never found the facetted pebbles 

 isolated, but always distributed among ordinary desert pebbles, 

 which lay close together. The annexed drawings show the 

 position of facetted pebbles with reference to other pebbles.* I 

 have frequently observed the movement of the sand between 

 such pebbles with strong wind (sand wind) and have come to the 

 following conclusion concerning the formation of the f acettes : 



" The sand flows along in little streams over the ground and 

 the pebbles lying on the surface form just so many obstructions 

 and resistances to the small sand-courses. In front of a large 

 pebble the sand-stream is parted, so as often to reunite behind 

 the obstruction ; often the divided streamlets run, isolated, some 

 distance further, finally reuniting with neighboring ones. In 

 consequence of this bifurcation and reunion of the small sand- 

 streams, caused by the stones lying on the ground, such stones 

 upon which two converging sand-streams strike, become provided 

 with two facettes, of which each has been formed by a sand- 

 stream. Since these facettes continually enlarge, they come 

 finally to an intersection (gegenseitigeu Schneiden) and form 

 thereby an edge. Pebbles which are constantly washed by 

 similar sand-streams, receive sharp edges ; but if the direction of 

 the sand-stream changes, then the edges and facettes will become 

 indistinct and again effaced. 



" In other words, planes are cut on the pebbles, whose develop- 

 ment forms edges, and on this account the word ' facetted-pebble' 

 (Facettengerolle) it seems to me best expresses the process of 

 their formation, for the edge is secondary." 



The attention which is paid to this subject in Germany and 

 the indications which point to even the slight action of wind- 

 blown sands are evident from what Karl v. Fritsch says in his 

 Allgemeine Geologie (Stuttgart, 1888), p. 302. 



" Wir konnen in Norddeutschland die grossen erratischen 

 Blocke an den Wegen, Bruckenfeilern, etc., nicht betrachten, 

 ohne wahrzunehmen, class sie last alle auf der nach der herrschen- 

 den Windiichtung (meist Nordwest) liegenden Seite hin eine 

 eigenthiimlich flachgrubige oberflache und einen starkeren Glanz 

 als liewartz zei^en. Giebt es audi solche Feldsteine bei denen 

 das erwahnte Verhaltnisse nicht wahrnehmbar ist, so kann man die 

 Ursache ihrer Rauhigkeit fast jedesmal erkennen. Sobald ein 

 erratischer Block eine langere Reihe von Jahre unverandert 

 liegen geblieben, fehlen diese spuren der Winderosion nicht." 



localities in which eolian action was observed in southern 

 New England : Island of Martha/ *s Vineyard. — At a number 



* The drawings are not reproduced in the present paper. 



