NEW FORMS OF CONCRETIONS 



By HENRY WINDSOR NICHOLS 



SAND-CALCITE CONCRETIONS FROM SALTON, CALIFORNIA 



A series of five sand-calcite concretions (Museum No. G, 1301) 

 presented to the Museum by Mr. Herbert Brown of Yuma, Arizona, 

 appear worthy of description. Regarding the conditions of the occur- 

 rence of these concretions little is known. Mr. Brown simply states 

 that they were handed him by a commercial traveler as having 

 been obtained by him at Salton, California. As there are extremely 

 large sand dunes in the immediate vicinity of Salton, it is probable 

 that the concretions were formed in these. Whether or not the form 

 represented by the specimens at hand is a common or an unusual 

 type in that locality is unknown. These concretions (Plate XIX) 

 are formed of sand cemented by calcite, and are, therefore, of the 

 type of the well known Fontainebleau and Saratoga Springs concre- 

 tions, from which, however, they differ in several respects. The Salton 

 concretions take the form of an irregularly botryoidal ball from which 

 projects a stout, tapering stem in such wise that the object assumes 

 the shape and proportions of an ancient mace. The change from 

 head to stem is abrupt, much as if the stem were driven into a hole 

 bored in the head, and there is even a slight annular depression in the 

 latter where the stem enters. The botryoidal appearance of the head 

 is due to a compound structure — each head being built up from a 

 number of spheroidal concretions grown together. While there is but 

 little flattening of the concretion as a whole, the subordinate spheroids 

 are much flattened and also elongated in the line of the principal axis 

 of the concretion. The specimens have a very rough surface from 

 the presence in large numbers of rhombohedral points of arenaceous 

 calcite crystals. These points suggest that these concretions, like 

 those from Devil Hill, Wyoming, described by Barbour,* are aggre- 

 gates of moderately large crystals. Lines of stratification (PlateXIX) 

 intersect the specimens in such a direction as to ind cate that the 

 principal axes lie conformably with the strata in which they form. 



* Bull. Geol. Soc. Amer, Vol. XII, p. i6s- 



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