Thoria Minerals from Llano County, Texas. 475 



numerous and extensive quartz veins extend to the surface. 

 Only in these veins have the ores of yttria, etc., been found 

 and only in the wider swellings of these veins or where they 

 have assumed the character of bold uplifts have masses of 

 large size been found. Here is to be seen a mound-like eleva- 

 tion 100 X 150 feet in area projecting boldly from the surround- 

 ing granite and 27 feet in elevation above the river terrace. , 

 It is made up of huge blocks and masses of quartz, and red 

 feldspar, all tightly massed together. The mound is nearly 

 circular in form and the contact with the country granite is 

 sharply defined. It is plainly seen to be a widening of a vein 

 that can be traced in a southwesterly direction for some dis- 

 tance and one of a series to be seen at several locations in the 

 near neighborhood. 



The quartz masses are from 5 to 20 feet thick, with the 

 interstices filled completely by a highly crystalline red feld- 

 spar. Between these irregular masses are found at times thin 

 seams of a black iron-mica and with this mica and in the adja- 

 cent feldspar are found the various ores of the rare earths 

 hereinafter to be noticed. 



From all sides this mound has been entered with trenches 

 and one or more of the yttria minerals have been found at 

 every opening. At this writing it has been so much cut into 

 by trenching that it is difficult to trace the original boundary. 

 On the river side the mound is rather steep but in other direc- 

 tions its sides slope gradually. Its top is flat and consists of 

 pure white quartz (bleached by weathering) and it is only on 

 the slopes and at the base that the several rare minerals show 

 themselves. The quartz and feldspar are very much stained 

 with red oxide of iron and some yellow and green uranium 

 compounds at the points where at present the larger mineral 

 masses have been found and these stains have constituted a 

 good guide to their discovery. 



Up to the present time we have identified the following 

 mineral species, but we will describe in detail only the more 

 important in the present paper. The list of species includes 

 quartz, hyalite, orthoclase, albite, biotite, muscovite, magnetite, 

 martite, gadolinite (several varieties due to alteration), fergu- 

 sonite (three varieties of hydrous species), allanite, molybde- 

 nite, molybdite, cyrtolite (several varieties), fluorite, gummite 

 (two varieties), a carbonate of the rare earths (tengerite ?), a 

 thorium-yttrium-lead uranate, a hydrous uranium thoro-silicate, 

 a yttrium-thorium silicate, a fetid gaseous compound (which 

 we first observed upon breaking some of the material for 

 analysis) and several minerals, found in small quantities, which 

 we have not had the opportunity, to identify with certainty. 



Quartz, is rarely found crystallized at this locality. Only 

 one pocket of smoky crystals (coated with ferric-oxide), of 



