3° 



Field Columbian Museum — Geology, Vol. III. 



poles. When compounded, they assume grotesque and imitative 

 forms. The nearest approach to the Salton forms is a double con- 

 cretion from Saratoga Springs (Plate XX, Fig. 2). This consists of 

 two cones with hemispherical bases. They are similar in form but 

 differ in size. The apex of the smaller is united with the base of 

 the larger. The length of the specimen is 38 centimeters and its 

 greatest diameter 8 centimeters. This may be considered as two 

 independent concretions which have grown together, and the larger 

 cone alone may be compared with the California specimens. This 

 larger cone is as smooth on the surface as the sand which enters into 

 its composition will permit. It is slightly curved. There is the usual 

 fold-like longitudinal swelling where it has grown faster in one 

 direction than another. The cone tapers gradually with no abrupt 

 change of curve from the widest portion to the apex. The relation 

 between the specimens from Salton and those from Saratoga Springs 

 and the Paris Basin are best brought out in tabular form: 



Comparison between Sand-Calcite Concretions from Three 

 Localities: 



Lack of data prevents discussion of the nature or origin of these 

 concretions from Salton, California. There is, however, one sugges- 

 tion which is called forth by the shape of these objects when they 

 are compared with some hitherto unrecorded forms of concretions 

 of an' entirely different character. The stem of any one of these 

 California specimens is very like a stalactite depending from the head. 



In certain sand dunes, notably in the "Hoosier Slide ' ' of Michigan 

 City, Indiana, flat sheet-like bodies of limonite concretion form in 

 certain strata of the sand. When these are dug out, numerous small 

 stalactites of limonite are found depending from their lower surfaces. 



