1824.] Scientific Notices — Mineralogy. 311 



posed of augite, naturally divided by fissures into fragments 

 easily separated by the pickaxe. The soil was strongly impreg- 

 nated with oxide of iron, and probably carbonate of lime. The 

 crystals were generally found on the edges and surfaces of the 

 fragments, but sometimes imbedded in carbonate of lime ; the 

 latter have generally a deeper green colour than the former. 



" A vein of green mica, about one foot in breadth, and several 

 feet in depth, passed through the rocks, on the borders of which 

 nearly all the crystals were found. When first taken from the 

 earth they broke with great ease ; on exposure, they soon hard- 

 ened, and when perfectly dry became quite firm. Their size 

 varies from extreme minuteness to five or six inches in circum- 

 ference ; their length from three-fourths of an inch to three 

 inches ; but some are both longer and larger. It was not 

 uncommon to find, on breaking; the larger crystals, small lumps 

 of oxide of iron and specks of mica within them, and in some 

 cases six-sided crystals of mica enter the sides of the sahlite 

 crvstals. Of the number of these no estimate can be formed : 

 there are thousands about the size of the finger, and myriads of 

 those which are smaller. The positions of the clusters are very 

 variable ; some, as has been remarked, are on the corners, edges, 

 and surfaces of the fragments of the augite rock ; others lie in 

 nests, like geodes within the surface. The crystals are grouped 

 together in numberless fantastic modes, intersecting, lying on 

 and passing through each other at all angles, usually without 

 producing any alteration in their respective forms. When, 

 however, one passes across the truncated edge of another, an 

 alteration in the depth of the truncation is often the conse- 

 quence. From a similar cause, and sometimes without any 

 apparent one, a very different and singular appearance is exhi- 

 bited — re-entering angles. These appear sometimes instead of a 

 truncation, and sometimes in the middle of one. In both these 

 instances, the faces containing the re-entering angle are parallel 

 to the sides of the primitive parallelopiped. Occasionally such 

 an angle, very obtuse, is produced by a truncation passing only 

 part of the way across the edge, when of course the angle is 

 contained by one face of the primitive, and the face forming the 

 partial truncation. It is not often that more than one of these 

 angles is found on a crystal ; occasionally two, which are gene- 

 rally on opposite edges of the primitive though I have found 

 one or two where they occurred on adjacent ones. A perfect 

 notion of all these cases will be conveyed by sections parallel to 

 the base. (See Plate XXXII, figs. 1, % 3, 4, and 5.) 



" Crystals ofthe form indicated by fig. 3, occur more frequently 

 than the others. It has eleven faces. Fig. 4 shows one with 

 fourteen. The terminations of these crystals are like those 

 which are eight-sided, and from an inspection of the laminae, 

 which are distinctly visible, they seem to be single crystals. I 



