_ 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,t 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,» 
29.17%; 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, % 
GS AD A er GG eae eae eo tse 5-40 
MASEL arth Nang cages 4 Grae hoticg hres Sab ibs VAhy Seo 36 
“Fontainebleau............ SO Die es ee eh ond 50 — 37 
Ree eG hs te. ROS pon re aN elie ee ie hs 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. 
+ Ibid.: p. 126; Warington: Physical Properties of Soil, p. 66. 
t Barbour: Bull. Geol. Soc. Am., Vol. XII, p. 165. 
§ Dana: System of Mineralogy, 6th ed., p. 266. 
