576 ESTLAND DUNES. 



posed comes in both principally from the bed of the sea being 

 brongbt to the surface in one case by the action of the wind and 

 the waves, in the other by geological upheaval. The sand of the 

 coast-dunes is rendered, to a certain extent, cohesive by moisture 

 and by the saline and other binding ingredients of sea-water, 

 while long exposure to meteoric influences has in a great measure 

 deprived the inland sands of these constituents, though there are 

 not wanting examples of large accumulations of sand far from 

 the sea- and yet agglutinated by saline material. Hence, as might 

 be expected, inland dunes, when not confined by a fixed nucleus, 

 are generally more movable than those of the coast, and the form 

 of such dunes is more or less modified by their want of consistence. 

 Thus, the crescent or falciform shape is described by all observers 

 as more constant and conspicuous in these sand-hills than in those 

 of httoral origin ; they tend less to unite in continuous ridges, and 

 ihey rarely attain the height or other dimensions of the dunes of 

 the seashore. 



Meyer describes the sand-hills of the Peruvian desert as per- 

 fectly falciform in shape and from seven to fifteen feet high, the 

 chord of their arc measuring from twenty to seventy paces. The 

 slope of the convex face is described as very small, that of the 

 concave as high as T0° or 80°, and their surfaces were rippled. 

 No smaller dunes were observed, nor any in the process of for- 

 mation. The concave side uniformly faced the northwest, except 

 towards the centre of the desert, where, for a distance of one or 

 two hundred paces, they gradually opened to the west, and then 

 again gradually resumed the former position. 



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 Oeological Report, Pacific Bailroad Rep., vol. 

 v., 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 Colo- 

 rado 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 at- 

 trition." 



The sands described by Mr. Parry and Colonel Emory are not from th« 



