*10 Outlines of the Mineralogy and Geology 



perfect vslaly structure. It reposes on Grcywacke at Brighton, 

 and is associated with it at Brookline, Newton and Needhain. 



y. A hed of very beautiful Amygdaloid is found in Grey- 

 wacke, at Hingham ; its basis is Wacke of a chocolate red colour, 

 inclosing nodules of Petrosilex; the colour of the nodules is 

 brownish red, and leek and olive green ; they are from the size 

 of a pcato that of an aim ond ; their fracture is fine splintery and 

 conchoidal ; sometimes the Petrosilex appears in small veins. 

 Some of the green nodules inclose Carbonate of Lime of a lami- 

 nated structure ; and they are sometimes incircled with red col- 

 oured Petrosilex ; and some are variegated with colours disposed 



veins. 



Variolite 



is a variety of Amygdaloid produced by the decomposition of the 

 basis, and the nodules project from the ma«s ; from the fancied 

 resemblance to the small-pox pustule, the name Yariolite* has 



been given to i 

 posed, and the 



nodules fall out^ or are decom- 

 ilar, and appears like lava. It 



found at Hingham, and in small quantities at Brighton. 



VII. GREYWACKE. 



I. This Rock, which geolists consider as the most important 

 in the transition class, is certainly the most interesting in this 

 vicinity. It is composed of nodules of Petrosilex, Quartz, Argil- 

 lite, Feldspar, Porphyry and Sienite ; some of these nodules 

 approach, in magnitude, to rolled masses, and from these we find 

 a gradual gradation to trains of sand. 



* Variola, small-pox. 



f 



