\\"lLD. — Mechanical Composition of So-called T.oixx at Titnaru. 287 



Haast, when he set forth his theory that this deposit is of aeolian origin, 

 followed Eichthofen's explanation of a supposedly similar deposit in China. 

 The required conditions are (1) the production of waste in an impalpable 

 form, (2) steppe conditions for its desiccation, (3) winds to transport it, 

 (4) vegetation to fix it where it settles. In our case it is presumed that 

 the material is rock-flour produced by the Pleistocene glaciers and brought 

 down by rivers ; and, since it is generally agreed that the extension of the 

 glaciers was due to the land being at a greater elevation, it is assumed that 

 the coastal plains then exhibited the characters of a steppe region, so that 

 the silt deposited on the flood-plains of the rivers was in condition for 

 transportation by the wind. Under these conditions winds also must be 

 granted. But now comes a difficulty. According to the experiments of 

 Udden,* the average largest size of quartz-particles sustained in air by 

 strong winds is 04 mm. in diameter, and Emersont says that 70 per cent, 

 of loess-particles range from 0-05 mm. to 0-01 mm. in diameter, a state- 

 ment that is apparently based on the following analyses given by Merrill. J 

 It is unfortunate that I have not been able to find any records of mechanica^ 

 analvses of the loess of China. 



Table II. — Mechanical Analyses of Loess and Dust. 



It will be noticed that mechanical analysis by the method generally 

 adopted in the United States separates the material into fractions that 

 differ somewhat in size from those obtained by the British method. 



Now, when we look at the composition of the Timaru deposit we find 

 that from 28 to 40 per cent, of the particles have a diameter ranging from 

 0-04 mm. to 0-2 mm., while there is also a certain small quantity of material 

 over 0-2 mm. in diameter. We have here, therefore, a very strong argu- 

 ment against the aeolian hypothesis. 



Richthofen further stresses the importance of vegetation as a means 

 of accumulating the fine particles. Haast quotes him as styling the loess 

 beds " a graveyard of innumerable generations of grasses." In the Geo- 

 logical Magazine, vol. 9, p. 297, 1882, Richthofen writes, " Where this dust 

 falls on barren ground it is carried away by the next wind ; but where it 



* J. A. Udden, Journ. Geol, vol. 2, p. 323, 1894. 



t F. V. Emerson, Jmirn. Geol, vol. 26, p. 532, 1918. 



t G. P. Merrill, Rocks, Rock-tveathering, and Soils, New York, 1906. 



