BADGERS TEETH AND BOARS TUSK 327 



the niter observed by Doctor Cross, is the only secondary mineral we 

 have observed in the amygdules. The aragonite occurs in platy crystals 

 and in tufts of needles. In the field we thought the needles to be some 

 zeolite, but they were kindly determined to be aragonite by Dr Austin F. 

 Rogers, of the Department of Mineralogy, Columbia University. The 

 dike also contains many inclusions of sandstone and shale. 



It would appear as if a dike had penetrated the Laramie in an east- 

 and-west fissure and had chilled. Explosive eruptions then broke out 

 along it and developed the agglomerate, into whose substance the dike 

 rock entered. The phenomena are similar to those which are met at the 

 well known Annie Lee mine, Victor, Colorado. It is, however, also pos- 

 sible that older eruptive rock than the dike existed on the surface and 

 was blown to fragments by the explosive action, so that its boulders 

 fell into the vent. The agglomerate must then have been penetrated b}^ 

 the dike or dikes, and all the rest of the sheet must have been removed. 

 The first hypothesis seems much the most probable. Whether the dike 

 rock is all the same mass or whether it forms several dikes is a fair 

 question. The general bearings of the exposures do not seem to run 

 together necessarily, but no continuation of the dike or dikes can be 

 found outside of the cone itself. In fact, the extremely limited character 

 of the exposure brings one irresistibly to the conclusion that it is an 

 elongated volcanic neck built up in a short fissure. 



A third hypothesis may be suggested. It is possible that a small mesa 

 with a cone once existed over the present neck, and that in this way the 

 agglomerate was formed. If so, we have an illustration of the conduits 

 which have fed the mesas. 



We name these exposures the " Badgers teeth " on the analogy of the 

 larger " Boars tusk," to be next described. 



The dike is wyomingite and one of the best examples of this rock in 

 the hills. The leucites are large and abundant. The diopsides are also 

 unusually large and well formed. The phlogopite has its own six-sided 

 boundaries. There is abundance of a yellow glass present in which the 

 other minerals are embedded. A very few stray sanidines were detected, 

 so that it can not be said that the rock lacks this mineral entirely. 

 Apatite is also present. The rock is practically identical with that at 

 the Boars tusk and Wortman dike. It is illustrated by figure 2 of plate 

 42. The figure brings out the coarse crystalline texture of the dikes as 

 compared with the flows. 



Boars Tusk 



This extraordinary volcanic neck is one of the most striking and in- 

 teresting of all the exposures in the region. It is in the middle of the 



