HOBBS .MINERALOGY OP WISCONSIN. 123 



ably colored ochre yellow by limonite in the pulverulent 

 form, and this material is sometimes found quite pure. Its 

 fine state of subdivision as well as its uniform distribution 

 in the pseudomorphs, makes it probable that its source is 

 the iron of the "black jack" which supplied the zinc to the 

 solutions, as has already been pointed out by Chamberlin. 1 

 The pseudomorphs of smithsonite after sphalerite which 

 are in the collection are of much less interest, since they 

 have the form simply of plates and spheroidal masses and 

 not of definite crystals of blende. 2 



GALENA FROM YELLOWSTONE, MINERAL POINT, HIGHLAND, 



GALENA, ETC. 



The crystals of Galena from this region are invariably 

 either cubes or a combination of the octahedron and cube. 

 On some specimens from Galena the rhombic dodecahedron 

 occurs as a small truncation of either the cubic or the octa- 

 hedral edge. The largest crystals come from the Yellow- 

 stone Diggings. The Yellowstone crystals are always 

 elongated, either in the direction of a principal axis, which 

 produces an apparently tetragonal combination (see 

 plate 6, fig. 2), or in the direction of a digonal axis, 

 which results in an apparently hexagonal combination 

 (plate 6, fig. 1). The length of these apparently prismatic 

 crystals may be several times their breadth. A crystal of 

 tetragonal habit in the University Collection has a length 

 of over a foot and a breadth and thickness of about four 

 inches. Another crystal with hexagonal habit is about 

 nine inches in length with transverse dimensions of about 

 four inches. The faces of these crystals are considerably 

 rounded from corrosion. The specimens which come from 

 Highland are quite symmetrical cubes with the cubic edge 



1 T. C. Chamberlin. The ore deposits of southwestern Wisconsin. Geology of Wiscon- 

 sin, Vol. IV, p. 396. (1882.) 



2 Dana states in his system (6th ed.) that pseudomorphs after crystals three inches or so 

 in diameter are found at Mineral Point. None are, however, contained in the University 

 Collection. 



