W. II. HOBBS — SECONDARY BANDING IN GNEISS. 



4< 51 



Archean division of the United states Geological Survey, in charge of Professor 

 Raphael Pumpelly. Mr. T. Nelson Dale, assistant geologist, lias prepared a mono- 

 graph on mount Greylock, in connection with which he has made an extensive 

 study of secondary foliation* A summary of his conclusions is contained in the 

 American Geologist for July, 1891. t 



The rock exposure illustrating the peculiar structural feature which forms the 

 subject of this paper is located east of the village of Great Barrington, near the 

 Hopkins-Searles dolomite quarry. The locality has already received considerable 

 attention from geologists. Professor Dana, in his first series of papers on the geology 

 of Berkshire county ,| printed a section passing through the locality, at which the 

 apparent unconformity of the limestone and gneiss was explained by a fault. The 

 portion of the section in question was printed on a larger scale as "section number 

 25 '* of Ins paper on Taconic rocks and stratigraphy.^ Tins is reproduced in figure 1 • 



Figure 1. — Section near Great Barrington (after Dana). 



Julien, in a paper entitled "On the Geology at Great Barrington, Massachu- 

 sctts," || has described the same locality. Mis views of the geologic structure are 

 expressed in figure 2. 



-yd*/ ii 



s, schi'bb or gneiss. q,q_uarUytc 

 d* d* clolomyfce. a , an- e-n-cieivt fault 

 Jo, 111. o f e 1-fcceii-t fa-ult. 



Figure 2. — Section near Great Barrington (pftei Julien). 



Mr. T. Nelson Dale,!] assistanl geologisl in the Archean division of the United 

 states Geological Survey, visited the Searles-Hopkins quarry al Great Barrington 

 on October 5 and 14, L889, and Mr. J. !•'. Wolff examined the gneiss later microscop- 



*Now in the hands of tlie public printer at Washington. 



I l'h' Grej lock Synclinorium : \m. Geol., vol. \ iii, pp. l-T. 



[ On the Quartzite, Limestone and Associated Ro -k- of the vicinity of Gri i( Barrington, B 

 shire eonnty, M if \m. Journ. Sci., 3d series, vol. v, 1873, p. 26, fig. 7. 



g On Taconic Bo lis and Stratigraphy, with i logical Map ol the Taconic Region : Vm. Journ. 



Sci., 3d Beries, vol. \ \ \iii, 1887, p. WO, with plate 1 1 . 

 Trans New Ifork Acad. 8ci., vol. v, 1887, p 



• i hi p ii i j i imIi and the ai npanying figure "■ were prepared for this paper by Mr. Pale. 



I.\ III Bui.ii, '■>.,,,. Soi . \m.. Vol .3 1891, 



