240 W. S. BAYLEY — SYENITES FROM NEW ENGLAND. 



dant of tho minerals imbedded in the sodalite are irregular grains of 

 plagioclase, little plates of lepidomelane and cancrinite, and a few small 

 Hakes of a brightly polarizing micaceous substance. Eleolite is often 

 intergrown with the sodalite in such a way that a large number of appar- 

 ently isolated areas of the former polarize together. The relation of the 

 sodalite to the other constituents leaves no doubt as to its age with respect 

 to these. It is certainly younger than any of them. Therefore, since it 

 is younger than components that are themselves younger than the eleo- 

 lite. and at the same time is intergrown with the latter mineral, as de- 

 scribed above, it must be an alteration product of this. The beautiful 

 pieces that have been sent to the museums as mineral specimens are cer- 

 tainly secondary, for in them the sodalite is found on the faces of joint- 

 cracks, and in most cases it extends back from these surfaces into masses 

 of eleolite that lie near them. 



The composition of compact masses of sodalite taken from seams in 

 the Maine rock was found by Clarke* to be : 



(0 = C1) 



The white alteration product of sodalite described by Dr. Clarke f under 

 the name of hydro-nephelite was not seen in any of the sections examined. 

 This is probably owing to the fact that the sections were all made from 

 pieces of the rock taken from the interior of blocks at some distance from 

 seams or joint cracks. Its microscopical description is so well given by 

 Diller J and Brogger,§ however, that little could be added to it by study 

 of material in the writer's possession. 



The cancrinite is not distinguishable from feldspar in ordinary light, 

 except in thick sections, where it possesses a slightly yellowish tinge. In 

 thinner sections it is colorless, transparent and without inclusions, other 

 than pores containing liquid inclosing movable bubbles. Of these there 

 are two kinds, viz, a series of long quadrangular and spindle-shaped cav- 

 ities arranged in lines with their long directions parallel to the vertical 

 axes of the cancrinite grains, and round and irregularly shaped ones 

 running in lines that are usually sharply inclined (often perpendicular) 

 to these axes. Under crossed nicols the mineral polarizes with very 

 brilliant colors, and extinguishes parallel to the two well marked cleav- 

 ages that traverse it. The grains, which are all allotriomorphic and 

 elongated in the direction of the lateral axes, are found intermingled 

 with the feldspar of the mosaic and in larger pieces scattered between 



* Am. Jour. Sei., 3rd ser., vol xxxi, 1886, p. 264. 



t Lbid., p. 265. 



t [bid., p. 266. 



\ Zeits. d. Kryst.. b. xvi. L890, pp. 234 and 636. 



