236 W. S. BAY.LEY — SYENITES FROM NEW ENGLAND. 



probable, however, that the eleolite preceded the plagioelase in its 

 crystallization. 



The only dark colored component visible is a dark green biotite,* 

 present not only in the large plates already mentioned, hut also as in- 

 clusions in the eleolite. In basal sections the mineral is so dark as to be 

 almost opaque. In other sections the ray vibrating perpendicular to the 

 cleavage is bright greenish-yellow, while that vibrating parallel to the 

 cleavage is dark green. The absorption, therefore, is a <L h = C. The 

 apparently uniaxial, negative interference figure opens slightly when 

 revolved under crossed nicols, and the extinction of the mineral is some- 

 times inclined to the cleavage about 1°. The composition, according to 

 Clarke,t is that of a very basic lepidomelane : 



In natural light the mass in which the lepidomelane is imbedded 

 appears as a colorless matrix, lor the most part transparent, but clouded 

 here and therewith opaque white and yellowish decomposition products 



of eleolite and the larger albites I figure 1. plate 7). Under crossed nicols 

 this apparently homogeneous groundmass resolves itself into large dull 

 grains of eleolite and albite, and a finely granular aggregate of brilliantly 

 colored feldspars and cancrinite, and a few perfectly isotropic grains of 

 sodalite. 



The eleolite. although it sometimes has a rectangular cross-section, is 

 usually in allotriomorphic grains, whose outlines arc rendered more or 

 less jagged by projections extending out into the areas between the sur- 

 rounding grains. The inclusions that crowd it are glass and fluid cavi- 

 ties, the latter frequently containing movable bubbles, long narrow plates 

 of lepidomelane, with their longer directions parallel to the vertical axes 

 of their host.-, and various decomposition products, among which may 

 he mentioned a few brightly polarizing fibers of some zeolitic mineral 

 and an occasional Hake of muscovite. Sodalite and cancrinite were also 

 met with, in a single instance, as alteration products of the eleolite; hut 

 since they were not entirely inclosed by this mineral they can scarcely 

 he spoken of as inclusions. Under crossed nicols many of the larger 

 grains are discovered to be intergrown with a twinned feldspar, which, 



* In spite of earn esl search through sixteen sections of the Litchfield rock, no trace of any mica 

 hut this could be discovered although both Rosenbuseh (Mikroskopische Physiographie, b. ii 

 L887, p. 85) ami Clarke (Am. Jour Sci., 3d ser., vol. xxxiv, 1887, p. 134) mention the exist snee of two 

 micas in it. In one section of tin- Cochnewagon rock the biotite is dark bi-own instead of dark 

 green. It presents tin' pleo shroism of ordinary biotite, and is certainly ao( a lepidomelane. The 

 rock is much decomposed, and is different in so many of its features from tin- other specimens 

 collected at this place, as well a- at the localities in Litchfield a in I West < rardiner, that its consid- 

 eration is entirely omitted from the present discussion. 



fAm. Jour. Sri.. 3d ser., vol. xxxiv. l.s.sV. p. 133. 



