File:The geology of Ascutney Mountain, Vermont (1903) (14783542752).jpg

Identifier: geologyofascutne00daly (find matches)
Title: The geology of Ascutney Mountain, Vermont
Year: 1903 (1900s)
Authors: Daly, Reginald Aldworth, 1871-1957
Subjects: Petrology
Publisher: Washington, Govt. Print. Off.
Contributing Library: Boston College Libraries
Digitizing Sponsor: Boston Library Consortium Member Libraries

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Monchique,Portugal. APIjITIC dikes CUTTIIS^G THJE SYEIflTES. Three kinds of acid dikes have been found cutting the various sye-nites of the area. Two of these are intimately related to the stockphases; the third has variant features. It may be noted that thereis an unusual lack of pegmatite veins both in the syenites and else-where about Ascutney, PAISANITE DIKE CUTTING THE MAIN STOCK. On the logging road running up from a sawmill on the northwestslope of Ascutney Mountain proper, toward the main summit, a dikewas discovered in the dark-green granular phase/of the Main stockat about the 1,600-foot contour (see PI. VII). The general trend of thedike is northeast-southwest, but at the road it bifurcates into twobranches^—^one, 40 feet (12 meters) wide, striking N, 40 E.; the other,50 feet (15 meters) wide, striking N. 25 E. The dike, as a whole, isvisible only for about 100 yards (91 meters); at each end its continua-tion is lost in the underbrush and talus of the steep mountain side.
Text Appearing After Image:
^;- llXi-i- 111 iD-;(jiCiUfflLiart;fBiii DALY.) PAISANITE DIKE CUTTING MAtN STOCK. 71 The rock is alight-tinted, pinkish-gray, pepper-and-salt, fine-grained,somewhat porphyritic aggregate of microperthite, soda-orthoclase,quartz, and alkaline hornblende, abundantly charged with basic seg-regations, with kernels of biotite and hornblende, and with pyroclasticfeldspars won from the coarse syenite through which the dike passedduring intrusion (spec. 139). The general habit is suggestively likethat of the porphyritic phase g of the Main stock, and we must believethat the two are products of the same magma. Yet, as we have seen,the implication that phase / and phase g are of different ages (theformer being cut by the latter) does not agree with the fact of obser-vation in the field. It is probable that there was not a great intervalof time between the intrusion of the Main stock and that of this dike. The dike is characterized by a conspicuous platy structure due tojointing, and, near its

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