18 Gregory — Volcanic Roe~k$ from Temiscouata Lake. 



volcanic rocks in Maine.* The inside filling of the amygdules 

 is silica or rarely calcite. The material next to the chlorite 

 lining is chalcedony, with well-developed mammillary struc- 

 ture. The center of the cavity is a mass of quartz grains 

 separated from the chalcedony by a definite boundary. It 

 thus appears that the amygdules were filled by three or four 

 successive periods of infiltration. 



Summary . — While the mere description of these rocks and 

 the determination of their volcanic origin is, in itself, chiefiy 

 of local interest, these facts have, however, important bearings 

 on the general geological history of the Atlantic coastal region. 

 That they are interbedded with Niagara sediments helps to 

 determine the time when wide-spread volcanic activity gave 

 rise to the numerous small areas of tuffs and lavas in the 

 Maine-Quebec region, while this fact throws additional light 

 on the physical conditions obtaining in that period. And 

 finally, the recognition of so much distinctly contemporaneous 

 volcanic material in well-bedded sediments affords another plea 

 for the stud} 7 of the sedimentaries by microscopic analysis. 

 * U. S. G. S. Bulletin 165, Plate sit. 

 Tale University, New Haven, Conn., March, 1900. 



