326 KEMP AND KNIGHT — LEUCITE HILLS OF AVYOMING 



just as on the Vesuvian lavas, and remind the observer most strongly of 

 some of the familiar phenomena of the Neapolitan volcano. It would 

 appear as if the second flow had followed the first after a comparatively 

 brief interval of time. The flows are not otherwise greatly contrasted. 

 They each have amygdaloidal and dense bands. The amygdules are 

 sometimes of altogether extraordinary size, being 3 to 6 inches long and 

 half as broad. They are oocasionall}^ lined with beautiful crusts of 

 chalcedony. 



The rock of this mesa is prevailingly, if not entirely, wyomingite. 

 Our specimens, gathered from the east and west ends and from cone 

 number 1, are of this type. There may be a little sanidine at the south- 

 west point, but it is rare and doubtful. Leucites are in great richness ; 

 diopside is comparatively scarce. There is a little hornblende and con- 

 siderable phlogopite. Rutile and apatite complete the list. Calcite ap- 

 pears rarely in the amygdules. The black scoria is of great interest. 

 In thin-section it presents a gray green glass with myriads of little leu- 

 cites scattered through it, precisely as in some Vesuvian scorias. We 

 have seen no similar rock anywhere in the hills. It has doubtless been 

 caused by the quick chill at the under side of the flow. The scoria may 

 be collected along the old and partially completed road at the soutliwest 

 corner of the mesa. 



Badgers Teeth 



These remnants of an old volcanic neck seem not to have been observed 

 by any geologist previously to our trip. They lie off the regular trails, 

 and are pretty well hidden in a gulch. They constitute five projecting, 

 tooth-like masses, ranged along an east-and-west line. The two on the 

 east are larger than the three on the west (see figures 1 and 2, plate 44). 

 From a valley eroded in Laramie sandstone a conical platform of the 

 same rock rises to a height of 50 feet. The sandstones strike north 

 70 degrees east magnetic and dip 5 degrees north. A talus of leucite 

 rock then ascends with a steeper angle about 75 feet farther, and from 

 this the two larger " teeth " project 20 or 30 feet additional. The hill is 

 from 500 to 600 feet in diameter at its base. The projecting masses con- 

 sist partly of a green, volcanic agglomerate and partly of solid eruptive 

 rock. The mass of the two larger teeth consists of about half of each. 

 Before the explosive activity which gave rise to the agglomerate there 

 must have been a solid dike, because the boulders of the agglomerate 

 are chiefly of eruptive rock themselves, and the interstices are filled wnth 

 tuff or mud precisely as at the Boars tusk. The dike is a dense drab 

 rock, which in places is amygdaloidal. The amygdules contain cr3'stals 

 of aragonite, which, except for the chalcedony of Steamboat mesa and 



