LS78. 



99 



[Frazer. 



Silica (SiO ? ) 



Alumina (A1 2 3 ) 



Iron Sesqui-oxide (Fe 2 3 ) 



Ferrous Oxide (Fe 3 ) 



Magnesia (Mg 2 0) , 



Lime ( CaO) , 



Soda (Na.,0) 



Potash (11,0) 



Manganous (MnO) 



Water 



100.11 



98.64 



In the following table the percentage of each constituent in Dr. Genth's 

 analysis of this trap is doubled, and the result compared with a column 

 showing the sums of the percentages of the average Labradorite, and the 

 average Pyroxene : 



Silica (Si0 2 ) 



Alumina (A1 2 3 ) 



Iron Sesqui-oxide (Fe 2 3 ) 



Ferrous Oxide (FeO) 



Manganous Oxide (MnO) . 

 Magnesia Oxide (MgO) . . 



Lime (CaO) 



Soda (Na.,0) 



Potash (K.,0) 



Water (H 2 0) 



Sum of La- 

 bradorite & 

 Pyroxene. 



198.75 



Double Per- 

 centage of 



Dr. Genth's 

 analysis. 



199.17 



It will be seen that the two columns agree remarkably well in most par- 

 ticulars, which is the same as saying that the composition of the rock is 

 very nearly what the chemical analysis of a mixture of one molecule of 

 Labradorite and one molecule of Pyroxene would show. 



In Report of Progress C, 18764 a number of similar traps were discussed 

 and analyses given ; amongst others of one from " West Rock," Connec- 

 ticut, and one from Beeler's farm, York County. 



The composition of the former, like the one here considered, agreed more 

 nearly with a distribution of Labradorite and Pyroxene molecules in the 

 proportion of one to one, while the "Beeler" trap corresponded more nearly 

 with the mixture of two molecules of Labradorite with one of Pyroxene. 



* 0.70 Ti 2 and 0.15 p. c. P 2 5 included in Si0 2 . 



t Ignition. 



J Second Geol. Survey of Penna. 



