SCIENTIFIC SURVEY. 259 



trap, leaving the dike as a high wall in the centre of the exca- 

 vation. 



A few other dikes were noticed in this region in other rocks. 

 Near Owl's Head Light House we saw a dike of quartz eight feet 

 wide, not perpendicular like those in the Eolian limestone, but in- 

 clined 10° S. 20° E. Pieces of the wall rock are found in it, as if 

 torn off and mixed in the fluid mass at the time of its injection. 

 Several quite large dikes of trap traverse the gneiss at Herring 

 Gut Light House in St. George. They run N. "70° E., the same as 

 the strike of the quartz dike. A small dike of white quartz, 

 running N. W. and S. E., cuts across the Taconic schists on 

 Negro Island in Camden harbor. Several dikes (or almost beds) 

 of trap occur in the Taconic schists and quartz rock in Belfast 

 harbor. 



6. Taconic Schists. 



We now come to the consideration of the last solid formation of 

 this region west of the Penobscot bay, the schists belonging 

 to the Taconic system. In Emmons' scheme these were called 

 " Magnesian slate," an inappropriate term, since both the term 

 slate is improper, and they contain no magnesia. In Vermont we 

 styled them Talcoid schists. But in Maine the Talcoid character 

 is very obscure, and in its stead we find the mineral mica abun- 

 dant. We do not suppose that it is essential to theory, that these 

 schists should every where be talcose in their appearance, because 

 they are so in Massachusetts and Vermont. At all events in Maine 

 so much mica is present frequently that they cannot be distin- 

 guished from the older mica schists, and on account of this diffi- 

 culty it will not be strange if we have improperly distinguished 

 between them in our geological maps, particularly in South 

 Thomaston. 



Three general deposits of these schists occur on the west side of 

 Penobscot bay ; first, those associated with the Eolian limestones 

 of Thomaston and Rockland ; second, a deposit la Camden ; and 

 third, a still larger deposit of interstratified schists and quartz rock 

 running south-westerly from Belfast. To expedite the description 

 of these deposits we will give a table of all the observal dips : 



