BOARS TUSK AND MATTHEW HILL 329 



larger stream in tins valley than the present Killpacker creek. In the 

 preexistence of solid lava which furnished most of the boulders, it is 

 necessary to believe by the same reasoning as is outlined above under 

 the Badgers teeth. We also conclude that a dike closed the eruptive 

 activity and forced its way through the neck. 



The dike at tlie Boars tusk, as has already been noted by Doctor Cross, 

 is wyomingite, and onl}^ differs from this rock as found in the flows by 

 the minor textural features which are characteristic of the dikes. Leucite 

 is the chief mineral in relatively large development. The diopsides are 

 likewise large. Phlogopite often forms composite crystals. The yellow 

 glass of the Badgers teeth is lacking. 



Doctor Cross has noted some slight contrasts between the leucite rock 

 of the agglomerate and that of the dike, mainly in the presence of large 

 apatites and leucites. He also detected a few small biotites. 



Matthew Hill 



This is a low rounded hill, located about a mile a little east of south 

 of Boars tusk. From a distance no one w^ould surmise that it was in 

 any way connected with the leucitic exposures. At its base it has a diam- 

 eter of about a quarter of a mile and rises 50 feet above the sandy waste 

 which surrounds it. There are small fragments of leucite rock scattered 

 about its base and also, to some extent, on its slopes. On the crest of 

 the hill there is a narrow dike 60 yards in length and having a strike 

 nearly northeast and southwest. This is separated from a small dike 

 having a course nearly at right angle to it by 15 feet of sandstone. A 

 short distance beyond the cross-dike there are two other dikes having a 

 strike of south 10 degrees west of north. The first one has a length of 22 

 yards and is separated by 10 feet of shale from the second, which extends 

 nearly to the base of the hill. The rock from all of these dikes is mostly 

 schistose, but there are occasional pieces of agglomerate, such as is found 

 at the Boars tusk and the other volcanic necks in this region. The hill 

 is unquestionably a volcanic neck that has suffered excessive erosion 

 which has not only cut down the leucite rocks, but also the surrounding 

 Laramie sandstone and shales. 



We take pleasure in naming it Matthew hill, after Dr William Diller 

 Matthew, of the American Museum of Natural History, whose work has 

 thrown much light on the paleontology and development of the so-called 

 lake beds of the Tertiary. 



The dikes are wyomingite in an advanced stage of decomposition. The 

 slides show spots of alteration, which are not infrequently distributed 

 through them and which are filled with sortie secondary and feebly re- 



XLVn— Bull. Geot,. Soc. Am., Vol. 14, 1902 



