Calcites from Rossie. 11 



one to three thin lamellae, twinned between crystals twinned parallel to 

 the O-face. 1 On account of the developing of one crystal more than 

 another, or the unequal development in different directions, forms, 

 though in reality quite simple, appear at first very complex. For 

 instance, a crystal iii the collection and which will be readily 

 recognized, has the appearance of two oblong rhombohedra placed 

 parallel to a cleavage face, while a third crystal lies in the re-entrant 

 angle. In reality two crystals are twinned parallel to the O-face, 

 and one is so developed that it nearly shuts in the smaller one. 2 



A peculiar feature of all crystals is that the E-faces of the primary 

 are all more or less roughened, the O-faces decidedly so, while the 

 other E-faces and the scalenohedral planes are highly polished. In 

 some crystals this seems to be simply due to etching, but in others to 

 a subsequent deposition of matter of less purity. In this latter case 

 the last addition has a milky opacity. Additions never seem to take 

 place on any but the primary rhombohedral and zero planes. 



Prof. Beck seems to infer that the roughness of these crystals is due 

 to incipient solution on the surface. The results of my studies lead 

 me to a different conclusion. A cleavage piece was taken from one 

 of these roughened crystals and placed under a low power objective. 

 The piece was then examined by reflected light. Focussing as nearly 

 as possible and turning a bright ray of light on the fragment, the 

 light was simultaneously flashed from a large number of the appar- 

 ently rough points. On turning the stage about 90°, the light was 

 again flashed from a large number of planes. As these planes were 

 parallel to the cleavage lines of the crystal, it appears to me that this 

 roughness must be referred to the regular development of the crystal 

 in a manner analogous to the striae on the prism faces of quartz. 



In case of the milky coatings, however, though the roughness is 

 again due to rhombohedral faces, there was evidently an interrupted 

 growth of the crystal. This is evident, since between the crystal and 

 its coating is a thin layer of iron pyrites. The secondary coatings are 

 not, however, always of a less degree of transparency than the body of 

 the crystal. In one or two instances the rhombohedron was devel- 

 oped, the growth interrupted, a deposition of cubical pyrite followed, 

 and finally the crystal received fresh additions, but each of the rhom- 

 bohedral planes was replaced by two sets of scalenohedral planes, 

 thus giving the crystal the appearance of a tetrahexahedron. There 



1 Twinned lamellae placed between the twinned crystals, fig. V, 



2 Fig. II gives a partial representation of this instance. 



