510 VARIETIES. 



There are of course several rocks not talcose, associated with the schists in the foregoing section. It will 

 give a good idea of the formation, and under the several general sections similar descriptions of this 

 formation will be found. The total thickness of the strata upon this particular section must be several 

 thousand feet. 



7. Quartz, Talc or Talcite, and Mica. This is generally called talco-micaceous schist. It may be 

 considered either as mica schist, which takes into its composition more or less of talc, or as talcose schist, 

 containing mica. Talc and mica resemble each other so much when disseminated in their corresponding 

 schists, that sometimes it is extremely difficult to say whether the specimen before us is micaceous or 

 talcose. Much of the talcose schist contains more or less of mica. This is more especially true in the 

 southern part of the State, in Massachusetts, and in parts of the east and west ranges in northern Vermont. 

 Indeed we have tried to show elsewhere, that a talcose schist (i. e. nacreous) may change into gneiss, and 

 thus the mineral resembling talc be changed into mica. We do not doubt but that the superabundance of 

 micaceous minerals, even in this formation, in the south part of the State, is an alteration from the more 

 perfect talcose schists, as the rocks grow more metamorphic as we proceed southwards from Canada line. 

 Specimens of these varieties are numerous upon the southern sections in the Cabinet. 



8. Talcose Schist, with carbonates of lime and oxyd of iron. Much of the talcose schist effervesces with 

 acid, indicating the presence of a carbonate. This is doubtless either a carbonate of lime, or of the 

 protoxyd of iron. Wherever the white carbonate of lime can be seen in the specimen, or near the locality, 

 no doubt can be entertained that the effervescence is due to carbonate of lime. In other cases, there is 

 reason to suppose that the additional mineral is carbonate of the protoxyd of iron. It is very common to 

 see decomposed masses of schist colored by iron rust. This probably results from the decomposition of this 

 mineral. It is said that this carbonate occurs where masses of quartz exist of considerable size. The 

 carbonate of lime is most abundant in the north part of the State; and there is reason to suppose that 

 still further to the northeast, the lime is still more plentiful. Connected with metamorphism, in some 

 way not fully understood, there is a strong tendency in nature to substitute silica for carbonate of lime, and 

 that sometimes quite abruptly. The talcose and mica schists strongly exemplify this statement in 

 Vermont. 



The carbonate of the protoxyd of iron is most abundant in the east part of the middle range of talcose 

 schist in the vicinity of the gold deposit, indeed the gold is found with the crystals of the carbonate. 



9. Talc (?), Quartz and Hornblende or Hornblende Schist. This variety is exceedingly common: forming 

 in the most thoroughly metamorphic portion of the formation, about one-fourth of the whole. It occurs as 

 a slate, as compact thick-bedded schists, as pure hornblende, as hornblende and quartz or feldspar, or as in 

 the heading. It may perhaps be true that a talcose schist will alter into hornblende schist. Along the 

 eastern margin of the middle range of the schists it is the most abundant. The mineral hornblende is 

 sparingly distributed over the whole formation. 



10. Talc (?), Feldspar and Quartz. This variety is intermediate between talcose schist and gneiss ; and 

 differs from the latter rock only by the substitution of talc for mica. It is obviously, however, a rock 

 more mechanical in its character than gneiss : the feldspar existing in coarse grains. This is found in what 

 we term a porphyritic talcose schist. Or it may approach gneiss in its character, especially near the 

 gneiss and gneissoid rocks of the Green Mountains. The feldspar may not be suspected to be present 

 e xcept by examining the edges of the strata freshly fractured. 



11. Novaculite Schist. This is a new term in geology. Novaculite however is an old term, and rather an 

 indefinite word also. It has been used to denote a variety of clay slate composed of silica, alumina and 

 an alkali. But mineralogists are always careful not to state much that is definite respecting it. We find 

 no mention of it in the latest treatises upon mineralogy ; and yet it is more worthy of mention than one- 

 fourth of the substances enumerated. It is regarded as a sort of unknown genus to which everything doubtful 

 can be thrown as to a general receptacle. We understand by the term novaculite what is popularly known 

 as honestone or whetstone ; a mineral of perfectly homogeneous but not crystalline structure, with the 

 composition (as before stated) of silica, alumina and alkalies, not very different from the most homogeneous 

 of talcose schists. It is generally unctuous like talc, and the purest portion of the novaculite would perhaps 



