22 



TRANSACTIONS OF THE 



[OCT. 19, 



T. 



ir. 



III. 



IV. 



V. 



VI. 



Total 



99.40 99.22 100.44 100.63 100.53 99.59 



I. Fairliaven, Vt. By .1. F. Kemp, Amer. Geologist, Aug. 1889, p. 97. 



II. Proctor, Vt. do. do. do. 



III. Campton Falls, N. H. G. W. Hawes, Amer. .Jonrii. Sci., iii, xvii, 14. 



IV. Montreal. B. .J. Harrington, Geol. Snrvey of Canada, 1877-78, p. 439. 



V. Forest of Dean, Orange Co., N. Y. J. F. Kemp, Amer. Journ. Sci., April, 



1888, p. 331. 



VI. Fort Montgomery, Orange Co., N. Y. By L. M. Dennis for J. F. Kemp, 



Amer. Naturalist, Aug. 1888, p. 694. 



The Monchiquites. 



The name monchiquite has been lately introduced by Rosenbusch^ 

 to include a group of dike rocks consisting of olivine, augite, horn- 

 blende, biotite (one or all three of the last named), and a glassy 

 base. It is derived from the Monchiqne Mts. in Portugal, where 

 such dikes were discovered in 18.50. In the further development of 

 the Lake Champlain dikes toward the extreme basic end of the 

 series there are a number consisting chiefly of zonal augite, small 

 brown hornblende and biotite crystals, and olivine, in an unresolv- 

 able base that is only very feebly refractive, if not actually glassy. 

 Yet some slides do show minute plagioclase crystals in the ground 

 mass, but not in sufficient development to throw them into the camp- 

 tonites. Magnetite is the only additional mineral. The augite is 

 the same as that described under the camptonites, and is in two 

 generations. It makes up at times almost if not quite the entire rock 

 and the analysis (No. 14) given below must indicate the approxi- 

 mate composition of this mineral. Magnetite is the only other com- 

 ponent of note. The hornblende is also like that of the campton- 

 ites, but when the second generation becomes very small it is very 

 difficult to distinguish it from biotite. In the altered portions of the 

 base they seem much more abundant than in the fresh, as they 

 stand out with very sharp definition. The alteration-product is 

 calcite. The hornblende in one or two instances replaces the augite 



1 M. Hunter and H. Rosenbuscli, Ueber Moncliiquit, ein Camptonitisclies 

 Ganggestein, etc., Tsch. Min. u. Petrog. Mitth., xi, 1891, p. 445. 



