Mica Slate. 335 



tempt has been made to give the actual number and extent of these 

 masses of granite on the map ; but simply to indicate where they are 

 most numerous. I regard the frequency of the protrusion of this 

 granite, and the perfection of its character, as some indication that the 

 formation is older than graywacke. A large proportion of the most 

 beautiful granite in the state is contained in this formation ; and it is 

 entirely wanting in hornblende; which circumstance, if I mistake not, 

 affords some presumption of its being among the oldest of the 

 granites. 



But does not the occurrence of anthracite in this formation at Wor- 

 cester, decide at once that it cannot be mica slate 1 Some might, in- 

 deed, doubt whether that mineral is actually contained in the rock 

 under consideration ; because the slate forming the immediate roof 

 and floor of the mine so much resembles clay slate. But its extent is 

 quite limited, and then succeeds the rock under consideration ; and I 

 have already stated that I regard the slate in which the anthracite 

 lies, as an anthracitous mica slate. This is not, therefore, the mode 

 in which I would dispose of the objection to my view of the nature 

 of this rock, derived from the presence of anthracite. 



But can there be any doubt that anthracite does occur in mica slate 

 and even in gneiss ? The highest European authorities are, I be- 

 lieve, unanimous on this point. If we consult the Tableau des Ter- 

 rains of Brongniart, we shall see anthracite marked in the stratum 

 of gneiss that lies next to granite ; in his Phylladique, a variety of 

 mica slate superior to the oldest variety of the graywacke series, &c. 

 " It has occurred," says Dr. Macculloch, "in gneiss, in micaceous 

 schist, in primary limestone, and in a conglomerate rock said to be- 

 long to the primary rocks."* " It was believed for a long time," says 

 De Lafosse, " that anthracite belonged exclusively to the primitive 

 deposites. But it has been since found that it abounds in the secon- 

 dary and transition formations," &c.f "Anthracite,'' says Prevost, 

 " belongs almost exclusively to the oldest of the deposites called tran- 

 sition ; where it is met with in beds or veins in the midst of mica 

 slate, of gneiss, and of the schistes-phyllades, which overlie vegetable 

 impressions of the family of ferns. For a long time, it is true, it was 

 said that anthracite was found in primitive deposites ; but it is proba- 

 ble that this term was applied to rocks and formations which are now 



* System of Geology, Vol. ii. p. 296. 



t Dictionnaire D'Historie Naturelle, Art. Anthracite. 



