55 



neutral silicates, one of a base containing 2 atoms of metallic radical 

 with three atoms of oxygen (alumina and peroxide of iron), the other 

 a silicate of such alkaline or earthy bases, as contain one atom of ra- 

 dical combined with one atom of oxygen (potassa, soda, lime, mag- 

 nesia (?) ), the oxygen contained in the silica ought always to be three 

 times that contained in all the bases ; while again the oxygen in the 

 alumina and peroxide of iron ought to be equal to three times that con- 

 tained in the other bases. He called attention to the fact, that this 

 latter is exactly the case in both of the above varieties, but that if the 

 oxygen contained in all the bases be multiplied by three, a small defi- 

 ciency of oxygen is made apparent in the silica of the first variety, 

 amounting to 1.6; (3x11-83=35.49;) but, that the deficiency of 

 oxygen in the second variety is so great, amounting to 5.6, (3x13. 

 22=39.66), that it cannot be accidental. Indeed, the proportion of 

 oxygen in the silica to that in the bases of this variety, may be near- 

 ly indicated as 2a to 1, (2ax13.22=33.05); thus leaving it uncer- 

 tain, in Mr. Boye's opinion, whether it be a different variety, or a 

 mixture of a felspar with an analogous subsilicate. The specimen 

 employed for analysis showed no signs of commencing decompo- 

 sition, though it would seem natural to connect the deficiency of silica 

 which it exhibited with liability to such a change. The analyses 

 also exhibit the fact, that the principal alkali in the first variety is 

 potassa, with a comparatively small proportion of soda, while the al- 

 kali in the latter is principally soda, with a small amount of potassa. 

 Mr. Boye proceeded to remark, that the rock which constitutes the 

 south-eastern portion of the primary formation of the state, differs in 

 many respects from the others, and has received the appellation of 

 the blue rock from its peculiar colour. The principal constituent of 

 this rock is a translucent felspar, of a bluish or smoky colour, which 

 sometimes in an irregular congregation constitutes the whole mass. 

 The rock affords, in many places, a very superior material for archi- 

 tectural purposes, and its principal constituent, the felspar, was there- 

 fore likewise subjected to analysis, with a view to compare it with the 

 two preceding. The result of this analysis was as follows : 



Felspar of the blue rock, from Quarryville, 3 miles N. E. of 

 Wilmington. 



Colour smoky gray, translucent; powder nearly white. Fracture 

 in mass irregular, coarse-grained ; that of distinct portions rhomboidal. 

 This variety of felspar exhibits, sometimes, a slight but indistinct play 

 of colours. Specific gravity in piece, 2.603, temp. 70° F. 



G 



