Maryland Geological Survey 155 



increased by the holding action of a plant tangle so as to equalize their 

 amount more with that of the very fine sand. 



Combining this conclusion with the stream character indicated by the 

 sharp rise of the " curve " on the left we have here a sediment deposited 

 where a stream discharged into or flowed through the midst of plants in 

 some small quiet body of water. Eegarding the grains of quartz in the 

 coarser sizes it should be borne in mind, not only for this sample but for 

 all others, that there is always the possibility, especially in near-shore 

 deposits such as these, that they have been brought in by wind. Thoulet ' 

 has shown the transporting power of wind, a strong gale (13 m. per sec.) 

 being able to carry grains over 1 mm. in diameter, and, while these theo- 

 retical deductions are somewhat invalidated by Udden's 2 observations on 

 wind deposits and his theoretical deduction that the effective force of the 

 wind is only that which survives the friction of the earth's surface (prob- 

 ably never exceeding 3 miles an hour), it is yet indicated by observation 3 

 as well as theory that an occasional coarse grain is brought in by winds. 

 This agent therefore may well be accountable for the few grains even of 

 the coarsest size found in this sample ; that a current which transports 

 material so very predominantly of the finest sizes should ever bring in 

 these few scattered coarse grains seems very improbable, while it is reason- 

 able to believe that an occasional strong wind would be quite able to 

 supply them. 



The rounding of these grains which, as noted above, is a marked 

 characteristic of many of the grains of the fine sand is a feature more 

 common in wind-blown than in water-transported sand, and therefore also 

 lends support to this conclusion. 



There is another feature of the sample, however, which is perhaps of 

 even greater stratigraphic interest than the evidence of the conditions of 

 its deposition. That is, the indications of weathering which its material 

 bears, and the absence of glauconite. Since other deposits of this type 



1 Thoulet, J., Analyse d'une poussiere eolienne de Monaco, etc. Annales de 

 l'lnst. Oceanograph. Tome iii, Fasc. 2, Paris, 1911, 8 pp. 



2 Udden, J. A., Op. cit. 



3 See Thoulet's observations, in the paper just cited, on sediments off the 

 Azores supposed to have been brought by wind from the Desert of Sahara. 



