PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 453 



Aporhyolite. Mesolite. Stilbite. Diabase.] 



No. 620. APORHYOLYTE. 



Eastern palisades. 



Ref. Annual Report, ix, page 58; Annual Report, x, page 59. Compare No. 230. 



Meg. The hand specimen is red in color, and is much fissured and in places 

 decayed. Small porphyritic quartzes and feldspars are embedded in an aphanitic 

 groundmass which shows distinct flow structure. 



.1//V-. In section the quartz phenocrysts are seen to be much corroded and some- 

 times show embayments of the groundmass. The feldspar phenocrysts are highly 

 altered and reddened and their species cannot be determined. The groundmass is 

 brownish red in color and in places appears homogeneous under a low power, but 

 under a high power it is seen to be not glassy, but is probably composed of very 

 minute quartzes and reddened feldspars, the product of devitrification. Some areas 

 show larger quartzes, probably of secondary origin. . Another section shows the 

 groundmass to be composed of small, irregular quartz areas holding the feldspathic 

 part of the groundmass poikilitically. 



Two sections. 



Age. Cabobian. u. s. G. 



No. 621. MESOLITE, ETC. 



Gathered from the beach at Lover's bay, S. W. % sec. 32, T. 61-1 W. (compare Annual Report, ix, page 50). 

 Ref. Annual Report, x, page 59. 



Meg. These pebbles are somewhat varied, but are of a light or pinkish white 

 color. They may be compared to Nos. 535B and 535C, and are probably from the 

 same general trap-sheet, which was apparently a surface flow, extending from 

 Cascade river, at least, to Good Harbor bay. 



No section. 



Age. Manitou. N. H. w. 



No. 622. STILBITE, MESOLITE, ETC. 



Mouth of False Poplar river; from the rock. 

 Ref. Annual Report, x, page 59. 



Mry. These zeolites have the color and cleavage of stilbite, and embrace a 

 small amount of what appears like mesolite. 

 No section. 



Age. Manitou. N. H. w. 



No. 623. DIABASE. 



From the upper layer of the point that encloses Eclipse beach on the east. This is two and a half feet 

 thick. 



Ref. Annual Report, ix, page 49; Annual Report, x, pages 59, 60. 



Meg. Medium grained, greenish gray, non-amygdaloidal, but chloritic from 

 decay. 



