k I 



MUSEUM OK COMPAII.VnVE ZOOLOGY. 



235 



than the similar substances lying outside the crystal, but often continu- 

 ous with them. Some of the crystals arc more than half filled in the 

 centre by a I'ectangular mass of this chlorite, often extending through 

 to connect with that outside. The space between the feldspars is occu- 

 pied by chloritic materials, opacite, etc., together witli some quartz. 

 Epidote and quartz occur in the groundmass as alteration products, and 

 transparent needles, frequently broken across, which are probably in part 

 apatite. Along the line of the conglomerate some of the feldspars are 

 bent. 



[3.] West End of Amygdaloid vevf/ near [1] 



Lens. A gray-colored groundmass, containing white and greenish 

 feldspar crystals, spots and crystals of epidote, occasional quartz and 

 epidote amygdulcs, and reddish areas of decomposition. — Section. Com- 

 posed princi])ally of feldspars, with considerable epidote, chlorite, opacite, 

 etc. The feldsjxirs are mainly plagioclase, but there are occasional 

 Carlsbad twins of sanidin. Some of the large porphyritic feldspars 

 arc broken and fragmentary; an effect, apparently, of the ilowing base, 

 for the small feldspars diverge, and flow around the large crystals. In 

 some cases tliey are seen to have been pnslied into the large crystals 

 a certain distance on opposite ends along the central line, while a line 

 of base passed through tlie crystal connecting the two tongues. Tliis 

 base, however, is now altered to calcite, chlorite, epidote, etc. Occasion- 

 ally two feldspars interpenetrate each other. The products of their de- 

 composition are the same greenish or colorless scales (which often have a 

 brilliant polarization), epidote, chlorite, calcite, quartz, and colorless nee- 

 dles. The smaller feldspars seem less decomposed than the larger ones. 

 Between the feldspars lie masses of chlorite, epidote, opacite, calcite, 

 magnetite, etc. ; often in the form of wedges between the divero-i 



One grain of altered olivine is seen in the section, identified l)y 

 the shape and the previously described motion of tiie aroundmass and 

 base around it. The exterior consists of reddish ferrite, penetrating 

 along the fissures ; the interior of quartz. ^ 



spars. 



-,mg fold- 



[4.] West End of the Avujgdaloid near [1] and [3], hut nearer in the Cen^ 



tre of the Mass. 



Lens. Similar to [_:^-]. ^ Section. The large feldspars are broken by 

 the base, as descri])ed above. Plagioclase and sanidin occur. True 

 amygdules occur here, recognized as such J)y the regular shape, and by 

 the fact that the small felds])ars of the groundmass flow around the 



