134 BULLETIN OF THE 



bearing traps in the Lake Superior region, where many of them were 

 composed of native copper; hence the name " spike amygdules," as given 

 by Pumpelly.^ Irving also mentions them from the same locality, and 

 Hawes refers to similar ones occuring in the trap of Connecticut as 

 " pipe-stem " amygdules.^ N ason notes their occurrence in the trap of 

 the Watchung Mountains in New Jersey,^ which Darton thinks is of ex- 

 trusive origin,* and Winchell reports them in greenstone from Thes- 

 salon Point, Ontario.^ Their occurrence in the lower trap of the 

 Tariif villa cut is restricted to a zone of little depth near the surface of 

 the sheet, where it may be supposed that escaping gases found the 

 easiest direction of expansion to be toward the surface ; hence their 

 peculiar position. A fortunate breaking of the trap may liberate one 

 of these rod-like amygdules ; they are composed of concentrically de- 

 posited calcite with a chlorite centre, or more rarely the chlorite centre 

 is wanting and the amygdule is now hollow. An occasional amygdule of 

 ordinary form associated with the spike amygdules is beautifully banded, 

 with its lamination parallel to the stratification of the sandstone above, 

 and hence dipping with it at the same angle, about twenty-five degrees 

 southeastward. Under the microscope, the bands are seen to be com- 

 posed of granular calcite and secondary quartz, the banding being due 

 to fluctuations in the supply of ferric iron during the process of filling 

 the vesicles. The lower part of the amygdules is extremely granular and 

 ferruginous ; the upper part usually consists of composite calcite indi- 

 viduals, and is free from iron. Some amygdules near the surface contain 

 grains of clastic quartz or orthoclase lying in the calcite filling, as is so 

 common in the eastern sheets, and arranged with the major axes of the 

 particles parallel to thebedding of the sandstone and lamination of the 

 amygdule. Cavernous amygdules with banded structure were also 

 found in the Farmington anterior ridge, locality 12. Their only other 

 occurreuce in this country as far as known, is in the amygdaloidal mela- 

 physe at Brighton, near Boston, Mass., where the great number and 

 essential parallelism of the bands to one another, and to the bedding of 

 the overlying slates, has been taken to indicate deposition of some kind 

 guided by gravity.^ In all these cases it may be fairly argued that 



1 Proc. Amer. Acad., XIII., 1877-78, p. 296. 



2 Amer. Journ. Science, IX., 1875, p. 191. 



3 Geol. Survey of N. J., Report for 1888, p. 37. 



4 Amer. Journ. Science, XXXVIII., 1889, p. 134. 



6 Geol. and N. H. Survey of Minn., XVII., p. 15, Plate I. 

 « Proc. Boston Soc. Nat. Hist., XX., 1878-80, p. 426 



