GEOLOGICAL IMPORTANCE OF DUNES. 
481 
indeed, so much resemblance between the effects of driving 
winds and of rolling water upon light bodies, that there would 
be difficulty in distinguishing them ; * but after all, it is not 
probable that sandstone, composed of grains thrown up from 
the salt sea, and long tossed by the winds, would be identical 
in its structure with that formed from fragments of rock 
crushed by mechanical force, or disintegrated by heat, and 
again agglutinated without much exposure to the action of 
moving water.f 
* Forclihammer ascribes the resemblance between the furrowing of the 
dune sands and the beach ripples, not to the similarity of the effect of wind 
and water upon sand, but wholly to the action of the former fluid ; in the 
first instance, directly, in the latter, through the water. “ The wind rip¬ 
ples on the surface of the dunes precisely resemble the water ripples of 
sand flats occasionally overflowed by the sea ; and with the closest scrutiny, 
I have never been able to detect the slightest difference between them. 
This is easily explained by the fact, that the water ripples are produced by 
the action of light wind on the water which only transmits the air waves 
to the sand.”— Leonhard und Bronn, 1841, pp. 7, 8. 
t American observers do not agree in their descriptions of the form and 
character of the sand grains which compose the interior dunes of the North 
American desert. C. 0. Parry, geologist to the Mexican Boundary Com¬ 
mission, in describing the dunes near the station at a spring thirty-two 
miles west from the Rio Grande at El Paso, says: “The separate grains 
of the sand composing the sand hills are seen under a lens to be angular, and 
not rounded, as would be the case in regular beach deposits.”— TJ. S. Mexican 
Boundary Survey, Report of, vol. i, Geological Report of C. C. Parry , p. 10. 
In the general description of the country traversed, same volume, p. 
47, Colonel Emory says that on an “examination of the sand with a 
microscope of sufficient power,” the grains are seen to be angular, not 
rounded by rolling in water. 
On the other hand, Blake, in Geological Report, Pacific Railroad Rep., 
vol. y, p. 119, observes that the grains of the dune sand, consisting of 
quartz, chalcedony, carnelian, agate, rose quartz, and probably chrysolite, 
were much rounded} and on page 241, he says that many of the sand grains 
of the Colorado desert are perfect spheres. 
On page 20 of a report in vol. ii of the Pacific Railroad Report , by the 
same observer, it is said that an examination of dune sands brought from 
the Llano Estacado by Captain Pope, showed the grains to be “much 
rounded by attrition.” 
The sands described by Mr. Parry and Colonel Emory are not from the 
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