Chiastolite. 



291 



Mineral Contents. 



The slate of the Taconic range sometimes contains octahedral 

 crystals of magnetic oxide of iron, as well as the sulphuret of the 

 same metal. 



The clay slate in Charlestown, is frequently traversed by veins of 

 crystallized quartz and calcareous spar. 



The most interesting mineral in this rock is the chiastolite, or 

 macle ; which is found in Sterling and Lancaster. There is a great 

 variety in the manner in which the prisms are disposed. The fol- 

 lowing are end views, of the natural size, of some of the most inter- 

 esting forms. 



This mineral is quite abundant in the clay slate in these towns, near 

 the place where the rock passes into mica slate. It changes insensi- 

 bly into the mineral which has been generally called andalusite ; and 

 the opinion of some of the ablest mineralogists of the present day,* 

 that macle and andalusite are the same species, derives support from 

 this locality. I have found this mineral in small crystals in a loose 

 mass of argillaceous slate in the town of Worcester. (No. 404.) 



Evidence of Disturbances in the Argillaceous Slate. 



I do not here refer to those agencies by which the layers of this 

 rock have been elevated from a horizontal to a nearly vertical posi- 

 tion ; nor to those by which its usual flexures have been produced ; 

 but to some movements that have taken place in certain anomalous 



* Beudant's Traite de Mineralogie, Vol. 2. p. 45. 



