226 Field Columbian Museum — Geology, Vol. i. 



disputed question as to whether the mineral crystallizes in the ortho- 

 rhombic or monoclinic system. Owing, however, to the incomplete- 

 ness of the crystals on account of their attachment, or to the stri- 

 ations on the faces, only one reliable set of measurements bearing 

 upon this point could be obtained. These were measurements of the 

 zone c:x:x' :c' =(ooi) : (201) : (201) : (001), as already quoted. Com- 

 pleting this zone by difference, the angles are : 



r.-.x = (ooi) : (201) — 71 52'. 



x:x' =(201) : (20i) = 36° 15'. 



x:c' —{t.6\) : (ooi) = 7i° 53'. 



Thus the brachydiagonal is an axis of binary symmetry and the 

 mineral must be regarded orthorhom- 

 bic. As noted by Busz also, the habit 

 of the crystals gives the impression of 

 orthorhombic symmetry. 



The usual development of the 

 crystals is shown in Fig. 3. ThSt[ 

 shown in the direction of the brachy- 

 diagonal is necessarily estimated, as! 

 no crystals doubly terminated in the 

 direction of this axis were found. The 

 general resemblance in habit to that 



of cerussite from Rezbanya* figured f ig- 3— caiedonite. 



by Schrauf will be noted. 



GAY-LUSSITE. 



SWEETWATER VALLEY NEAR INDEPENDENCE ROCK, WYOMING. 

 MUSEUM No. E 9695. 



On dissolving in water the native carbonate of soda found in the 

 Sweetwater Valley, Wyoming, a residue of clay and minute crystals 

 is left. Some of the latter were kindly forwarded to the writer by 

 Prof. W. C. Knight of the University of Wyoming, who was the first 

 to notice the crystals, so far as I am aware. A test of the pyrognos- 

 tic and crystallographic characters showed the crystals to be undoubt- 

 edly gay-lussite. They are microscopic in size, none that I found 

 being as large as the head of an ordinary pin. More exactly, none 



♦Dana's Mineralogy, p. 287. 



