1875.] 



409 



[Frazer 



CHEM. UNITS. 



Total chemical units of oxygen * 5 .565 



Excess of units of acid over basic radicals (= units of 



saturating oxygen) ............... 1.465 



4.100 



Linking oxygen 



= 33.80 p. c. 

 Saturating Oxygen = 11.72 p, c. 



Hence the conclusion that 4.09 p. c, of this rock is Silicon combined 

 as ortho-silicic acid, according to the formula M'^Si'^ O"^, and the re- 

 maining 20.51 per cent, exists in the form of the mouo-meta acid, or as 

 M'jSi'^ 0"3. 



The excess of the chemical units of Si, over those of the basic radi- 

 cals, will also serve to explain the fact (mentioned to me by Mr. Hawes in 

 reference to the Ct. Traps, but which I have not yet sufiiciently verified 

 in those from our own State), that in many cases free Silica is observed 

 in them. 



It may be added that the reduction of the analysis of these rocks to a 

 form which gives the measure of chemical force employed in the com- 

 position of their constituent minerals, and in a single unit, i. e., the 

 ratio of the percentage weight by the equivalence to the atomic weight, 

 seems a very convenient one to employ in discussing the questions here 

 considered. 



It is interesting to observe that while the analysis of the Connecticut 

 Dolerite agrees very well with a mixture of one molecule of Labradorite 

 to one of Pyroxene, that from Beeler's farm corresponds even more closely 

 with a mixture of two molecules of Labradorite to one of Pyroxene. In 

 this table the same analyses of Labradorite and Pyroxene are used as in 

 the former case. 



3 molecules of Beeler's 

 dolerite. 



Si. 



24,65 X 3 



73,95 



i 11.81X3 

 AI2 &«• 



35.43 



Dyad and 1 18.45 X 3 



Monad [ 



Basic I 

 Kadicals, j = 55.35 



A. p. s. — YOL, xiT. 3a 



49,40 (24.7 X 2) 2 molecules of Labradorite. 

 24.34 1 molecule, Pyroxene. 



73,74 



32.40 (16,2 X 2) 2 molecules, Labradorite. 

 1.88 1 molecule, Pyroxene. 



34.28 



23,60 (11,8 X 2) 2 molecules, Labradorite. 

 30.40 1 molecule, Pyroxene. 



54.00 



