472 W. Cross — Alunite and Diaspore 



through, the prominence of a pinacoid. While these various 

 forms were thought to belong to a single mineral, the species 

 was not recognized in the field. By measurements, on a small 

 Fuess goniometer, the mineral was, however, readily identified 

 crystallographically with diaspore, and the faces determined as 

 follows : go P 66, prominent in all_ crystals ; go P2, the most 

 prominent prism ; go P, narrow ; P2, broad, good faces ; unit 

 pyramid, P, narrow ; P ob, occasionally distinct. As this 

 seems to be the first known occurrence of diaspore in any such 

 connections, and also on account of the rarity of this crystallo- 

 graphic development, the writer requested Dr. W. H. Melville 

 to examine the material carefully, and if the result warranted 

 it, to present the crystallographic data, with figures, in a special 

 article. This he kindly consented to do, and his report will be 

 found in the paper succeeding this. A small clump of clear 

 crystals was analyzed by Mr. Eakins with this result : 



A1 2 3 83-97 



H 2 15-43 



99-40 



The results of the crystallographic al and chemical examinations 

 thus place the identity of the mineral with diaspore beyond 

 question. Further data as to the occurrence will be given in 

 discussing the origin of these minerals. 



IV. Alwute fjseudomorphs. 



At the western base of the Posita hills a shallow prospect 

 shaft has been sunk in a brecciated quartzose vein matter, 

 which is the alteration product of the country andesite on a 

 line of Assuring. Near by is a large dike of altered rhyolite, 

 the specimens from it which have been examined consisting of 

 kaolin and quartz. 



The shaft has long been abandoned and is inaccessible. Its 

 dump shows mainly quartz vein matter through which some 

 jjyritiferous ore is sprinkled. One small part of the dump is 

 made of bluish quartz breccia, the spaces between angular 

 fragments being lined by crystals. There is first a coating of 

 minute quartz prisms, then in some cavities larger quartzes with 

 rough prismatic and smooth pyramidal faces. In a portion of 

 this material there are numerous tabular crystals, and, of deci- 

 dedly later age, kaolin, or ochreous limonite, in a few specimens. 



The tabular crystals referred to are dull white, opaque, with 

 rough surfaces, yet showing distinct crystal form. The faces 

 are to be interpreted as unequally developed positive and nega- 

 tive rhombohedrons, combined with a dominant basal plane. 

 In size these crystals average 0'5 cm in width, by a thickness of 



