468 WARREN AND POWERS DIAMOND HILL-CUMBERLAND DISTRICT 



Sneech Pond, in an irregular patch a mile farther east, in a small knob 

 on Hunting Hill, and on a small hill west of Hunting Hill. Emerson 

 and Perry found a dike of somewhat similar character near Lonsdale, 4 

 miles southeast of Albion. 



The Cumberland dike is about 75 feet wide and about a mile long and 

 of steep dip. It is intrusive into the Ashton schist, except at its southern 

 end, where it cuts the quartzite. Small inclusions of the schist are abun- 

 dant near the walls of the dike and some quartzite inclusions are also 

 present. The dike shows but little chilling at the contact, and, as noted 

 by Emerson and Perry, fluorite is often abundant in the sediments at the 

 contact. In one place, where the road from Arnolds Mills cuts through 

 the dike, a quartz vein a foot wide is exposed for a distance of" nearly 50 

 feet along the strike of the dike. Part of the quartz is filled with long, 

 slender needles of blue riebeckite (crocidolite) and furnishes ver}' at- 

 tractive specimens. Fluorite is often abundant as dark purple masses 

 up to lYo centimeters in diameter. With the fluorite are a dark sphaler- 

 ite, galena, and chalcopyrite, the latter crusted with covellite. The same 

 sulphides associated with fluorite. it is interesting to note, are also found 

 in quartz veins and in the pegmatic phases of the Quincy granite. 



The specimens of the porph}Ty from this dike examined by the writers 

 show a dark gray rock containing rather abundant round, smoky to blue 

 cjuartz phenocrysts and rectangular feldspars embedded in a dark, fine- 

 grained groundmass. The porphyry has been strongly sheared, giving 

 the impress of a flow structure. The phenocrysts of feldspar, so fai> as 

 seen, are a microperthite (pretty strongly altered), although Emerson 

 and Perry**^ state that they have observed soda orthoclase; also pheno- 

 crysts filled with crystallizations of acid plagioclase. The groundmass 

 in all of the specimens examined by us consists of a fine mixture of 

 microperthite and quartz in which there is a great amount of magnetite 

 in clustered masses of small grains and as separate grains and dust ; also 

 much calcite and other secondary products. Fluorite is always present. 

 A small amount of what appears to be aegirite remains and some riebeck- 

 ite may be seen in sections from some of the outcrops, but practically all 

 of the soda-iron silicates have gone over to magnetite. The habit of the 

 magnetite suggests that riebeckite was strongly predominant. 



In the irregular mass of porphyry one mile east of Sneech Pond the 

 quartz phenocnsts are rather larger than in the dike, and with the less 

 conspicuous feldspar crystals lie in a fine groundmass which is highly 

 altered and, besides quartz and feldspar, contains magnetite, sericite, 

 calcite, and a greenish -brown secondary biotitic product. 



Loc clt.. p. 62. 



