June, 1906. New Forms of Concretions — Nichols. 27 



meshes to the inch. It appears that the closeness with which the 

 sand packs itself has some bearing upon the nature of the concretion. 

 A sand of similar physical constitution was prepared from a mixture 

 of glass sands by the use of sieves. This sand was packed into a 

 glass cylinder and compacted by long tapping of the outside of the 

 cylinder by a stout wooden rod. This sand, so compacted, enclosed 

 between its grains 40% of voids which were calculated by the usual 

 formula.* 



Such a sand undisturbed in its natural bed may be assumed to 

 compact itself in time somewhat more than it may be compacted by a 

 few minutes' tapping in the laboratory. Such undisturbed sand beds, 

 according to King and others, f contain 35% to 40% of pore space. 

 Therefore if a sand-calcite concretion is composed of calcite filling 

 voids previously existent between grains of sand, it will have by 

 volume a composition of calcite 35-40%, silica 65-60%. The com- 

 position by weight will be approximately the same, as the specific 

 gravities of the minerals differ but little. Such a composition has in 

 fact been proved by the only two determinations of this character 

 known to the author for similar concretions. These were carried out 

 upon material from the two widely separated localities Devil Hill, 

 Wyoming,^ and Fontainebleau, France. § 



A determination of the percentage of sand and calcite in the 

 Salton concretions was made upon material broken from the stem. 

 The fragments were treated with cold dilute hydrochloric acid and the 

 insoluble sand weighed. The concretion was found to contain: sand, 

 20.17%; calcite, 70.83%. This corresponds to a composition by 

 volume of about: calcite, 70%; sand, 30%. The above facts may be 

 tabulated as follows: 



Composition by Volume of Sand-Calcite Concretions from 

 Three Localities: 



Sand, % Calcite, % 



Theory 65-60 35 - 40 



Devil Hill 64 36 



Fontainebleau 50-63 50 - 3 7 



Salton 30 70 



From this table it appears that in the Fontainebleau and Devil 

 Hill concretions the calcite is little, if any, in excess of that required 

 to fill the voids between the sand grains. The Salton concretions, on 

 the other hand, have but half the sand and twice the calcite required for 



♦King: Physics of Agriculture, p. 115. 



tlbid.: p. 126; Warington: Physical Properties of Soil, p. 66. 

 % Barbour : Bull. Geol. Soc. Am., Vol. XII, p. 165. 

 § Dana: System of Mineralogy, 6th ed., p. 266. 



