FEANKLIN BUTTES. 491 



Hamilton Butte, which forms the northern end of these two ridires, is 

 a broad, flat-topped hill, a little over 3,000 feet in height, measm^ed from 

 its base, wdth long, gentle, well-covered slopes, made up of limestone beds 

 belonging to this same formation, lying nearly horizontal, but with an incli- 

 nation of a few degrees to the westward. The same fossiliferous stratum 

 was recognized here as in the ridges to the south, in which was also found 

 the Productus suhliorridus of the Egan Mountains. In the northern end of 

 Butte Valley, at the base of Hamilton Butte, are numerous large springs of 

 fresh water, surrounded by considerable extents of meadow-land. 



Feakklin Buttes. — Out of the desert plain to the north of Hamilton 

 Butte rise three little hills, known as the Franklin Buttes. With the excep- 

 tion of a little fragment of limestone on the eastern end of these hills, which 

 has been referred to the Lower Coal-Measure limestones of the Egan Mount- 

 ains, they are entirely made up of older eruptive rocks, which form a series 

 quite as peculiar and very similar to those of the Kinsley district. 



The rocks which form these little buttes present an interesting grada- 

 tion from a syenitic granite, through granite-porphyry, into genuine felsite- 

 porphyry. The western or smaller of the three has not been visited, but is 

 colored like the main mass of the middle of the group. This butte consists 

 of a long, narrow, north and south ridge of syenitic granite, on whose east- 

 ern spurs are a succession of different beds, or dikes, of granite-porphyry, 

 having also a north and south trend, though the hills are too low and 

 too much covered by surface debris to show very definitely their struct- 

 ure. The eastern or higher butte shows a much more felsitic-looking 

 rock, with less variety of structure; its main mass being a genuine felsite- 

 porphyry. 



The main rock of the middle butte is a crystalline aggregation of flesh- 

 colored orthoclase, and greenish plagioclase-feldspars, quartz, and horn- 

 blende, in almost equal proportions, with some titanite. In places, it shows 

 a porphyritic tendency in developing a partial groundmass, Avith somewhat 

 rounded particles of quartz, and has been classed by Professor Zirkel from 

 the hand-specimen as a granite-porphyry. The succeeding dikes, or beds, 

 to the eastward, of which no less than six varieties were observed, are dis- 

 tinctly syenitic granite-j)orphyries. 



