Hidden — Mineral Research in Llano Comity, Texas. 431 



material yet analyzed showed (vide Hillebrand's analysis) 

 4'31 H 2 present, it is possible that these little bright spots 

 are only the normally pure anhydrous mineral. It is tenable 

 also that these little inclusions, with their high radio-activity, 

 are but a normally pure form of nivenite in which only U0 2 

 is present. Since mackintoshite can be rationally interpreted 

 as being a mixture of three parts of thorite with one of uranin- 

 ite (nivenite), the assumption that a new mineral has been dis- 

 covered may not stand. The question is certainly one of 

 unusual interest at this time and merits further investigation. 



Thoro-gummite. — Contact radiographs of this mineral, made 

 from a flattened surface after forty-eight hours exposure, in the 

 dark, had much the appearance of ordinary sunlight photo- 

 graphs. All the minute details of structure and varying 

 degrees of radio-activity were beautifully portrayed. It was 

 surprising to note how perfect a picture this mineral could 

 make of itself without any outside aid other than a photo- 

 graphic plate and a long exposure in the dark. 



Masses up to a pound weight were found, and this proves 

 that mackintoshite will not be as rare as it is now, when the 

 mine is worked down to lower levels ; for thoro-gummite is 

 only an alteration product of mackintoshite, it having assumed 

 one more molecule of water and changed its U0 2 to U0 3 , and 

 its, color from an apparent jet-black mineral, of specific gravity 

 5 '50, to a dull yellow-brown mineral having specific gravity 

 4-54+ . Long square prisms, like those of zircon, with simple 

 terminal pyramidal planes, were observed. 



Yttrialite.— This species gave better radiographs from its 

 altered red crust and its yellow ochreous variety than from the 

 pure dark gray-green anhydrous mineral. All of its radio-activ- 

 ity must emanate from the ten to twelve per cent of thoria pre- 

 sent. Hillebrand's last analysis has shown that its composition 

 can best be interpreted by assuming that it is a mixture of an 

 yttrium silicate with the thorite molecule (both anhydrous). 

 Slabs of this mineral eight inches long and six inches broad 

 were broken from some of the larger masses, thus affording 

 fine opportunity for large experimentation in testing it radio- 

 graphically. 



Fergusonite. — The mono-hydrated variety made the best 

 radiographs, but all the varieties (of which there are four at 

 the locality) showed more or less action upon the sensitive film. 



A new association was discovered in this species. Symmet- 

 rically compounded crystals of nivenite with fergusonite were 

 found in the south walling of the hill. Long square prisms of 

 nivenite with flat terminations, had in their centers an equally 

 long but tapering pyramidal crystal of fergusonite, in parallel 

 position. Some of these were one inch long and one-quarter 



