Minerals in Gneiss. 395 



Yet the direction is pretty uniform, being usually north and south. 

 And in respect to the dip, I think it obvious that a westerly dip pre- 

 dominates, being rather largest towards the western side of the range. 

 Thus is it represented on Plates XVII. and XVIII. From those 

 sectional views, it will be seen that this westerly dip is most uniform 

 across the southern part of the range. In the central section, the dip 

 becomes east towards the western part, and still more so in the most 

 northerly section. 



The smallness of this dip in many places is another striking cir- 

 cumstance in this same range. If we have any rock that would be 

 selected for the oldest described by geologists, it is this gneiss : and 

 hence we see how deceptive was the old rule, which taught us that 

 the relative ages of rocks might be determined by their dip. 



Mineral Contents. 



In some parts of the world gneiss is remarkable as the repository 

 of a number of the precious stones. In Ceylon, for instance, where 

 gneiss is the prevailing rock, it contains of the quartz family, rock 

 crystal, amethyst, rose quartz, cat's eye, prase, and hyalite : also topaz, 

 schorl, pyrope, cinnamon stone, zircon, spinelle, sapphire, and co- 

 rundum.* Hitherto the gneiss of Massachusetts has not yielded so 

 rich a supply. But it affords enough of the same minerals, to prove 

 a strong analogy between the causes that produced these deposits in 

 parts of the globe so widely separated. Especially will this be true, if 

 we regard the limestone beds in the northeast branch of the Worces- 

 ter gneiss range, as a part of this formation ; and this is certainly 

 reasonable. For in these beds have been found spinelle, a garnet 

 which is probably cinnamon stone, asparagus stone, nephrite, and 

 precious serpentine : and the following statement will show that sev- 

 eral others of the Ceylon minerals have also been found in the gneiss 

 itself. 



By far the most important mineral hitherto found in our gneiss, is 

 graphite. As described in the first part of my Report, its most impor- 

 tant locality is in Sturbridge. It occurs in other places, however, as 

 in North Brookfield, in Brimfield, in Hinsdale and New Marl- 

 borough; though I am not sure that in the two last named localities, 

 the gangue is gneiss, The plumbago in Sturbridge, which is situated 



* Geological Traasactions, vol. 5. p. 318. 



