of Boston and its Viciniiif. 



«09 



almoiul-shappd hence tlie name of this rociv from the Latin, 



which in some specimens verj 



Amygdala. The basis is Wacke, 



much resembles some varieties of Greenstone, 



II. The imbedded minerals are Petrosilex, Quartz, Feldspai 

 Epidote and Carbonate of Lime. The predominant 



colour 



basis is brownish purple red^ but wbeu it approaches to Green- 



stone^ it verges to greenish 



grey 



The Quartz is the most 

 abundant of its imbedded minerals^ next is the Carbonate of 

 Lime, next Epidote^ while Feldspar and Petrosilex exist only 

 in small quantity. These minerals present their usual characters^ 

 but the aspect of the rock is very much modified by their size^ 

 which varies from that of a pin^s head to tliat of a pea 5 those of 

 similar magnitude are generally grouped together^ and frequently 

 the transition from the minute to the larger grains is very abrupt. 

 III. Not only are simple minerals imbedded in Wacke^ but 

 these minerals themselves frequently inclose each other. The no- 

 dules of Quartz are sometimes hollow, and the cavity is studded 

 with minute crystals of Epidote, and sometimes 

 cles Quartz, vi?ith a beautiful green belt, 

 are sometimes perfectly foliated, and nea 



latter 



centre, 



/ 



their circumference is fi 



The nodules of Lime 

 'ly transparent at their 



and opaque. 



ranuiar 



1 



The Epidote in the variety which 



crystal of Sulphuret of Iron ; Hornblend 



some- 



times, but very rarely, found io this Amygdaloid, and there are 



of Talc and of Muriate of Copper. Quartz 



and it is in them 



Iron Mica is principally 



found. 



IV. Like the other rocks which have been described, it appears 

 to be destitute of stratification, but it sometimes presents an im- 



f 



