802 PROCEEDINGS OF THE AMERICAN ACADEMY 



quartz contains naany fluid cavities, some with movable bubbles. None 

 of the bubbles showed any change when heated to 100° C. 



MATRIX. AMYGDULES. 



(I.) 1. Plagioclase. 2. Pykoxkke ? 



(II.) Wholly changed 



to PKEHNITE. PeEHNITE. 



(III.) 1. Soft, yellowish-green substance. 2. Calcite. 



(IV.) Epidote. 



(V.) QUAKTZ replacing calcite ami enclosing 



the prismatic green earth. 



The chloritic matrix passes gradually into the quartz matrix, which 

 forms the middle zone of the specimen. This consists of purple-brown 

 compact quartz, in which no crystal -faces occur. This portion breaks 

 with sub-conchoidal fracture. It abounds in amygdules of white quartz 

 and green epidote, the latter sometimes in crystals -j^j inch long, im- 

 bedded in quartz. The amygdules are, in places, half quartz and half 

 calcite. 



In thin sections the matrix shows the usual feldspar outlines, filled 

 with a limpid colorless substance, and surrounded and sharply defined 

 by a soft, impellucid, iron-stained substance. Some of the characteristic 

 pseudomorphs after pyroxene also occur. 



But in polarized light the bulk of the rock is seen to be quartz, with 

 very coarse granular aggregate polarization, so coarse that each integral 

 grain encloses and fills many feldspar outlines. 



In parts of the sections this office is performed by prehnite in the 

 same manner as by quartz. But this is evidently only a fragmentary 

 residue. We have here on a large scale, in the whole matrix, what 

 we saw in the other part of the specimen only in amygdules ; here the 

 formerly wholly prehnitized mati-ix has been almost entirely changed 

 to quartz, perhaps after going through an intermediate change to cal- 

 cite. Here, too, the quartz encloses large numbers of the delicate 

 prisms of epidote-like substance. 



An analysis of this part of the specimen, by Mr. Geo. "W. Hawes, 

 gave, as a mean of two analyses, — 



Silica 51.42. 



Alumina 13.38. 



Ferric oxide 9.59. 



