BASIC VOLCANICS OF HEMLOCK FORMATION. 



107 



TABLE II.— MOLECULAR PROPORTION OF THE CHIEF OXIDES. 



TABLE III.— ATOMIC PROPORTION OF METALS. 



As tne calcium increases there is a corresponding increase of magne- 

 sium and a diminution in potassium. A decrease in sodium is also shown 

 if Nos. 1 and 3 alone are compared. The percentage of sodium present is 

 rather high and with the potassium indicates a magma family rich in alkalies. 

 The magnesium is notably high; such high percentages as we have here 

 usually accompanying much lower percentages of alkali. It may also be 

 noted here that the presence of the magnesium in such amounts indicates 

 the former presence of olivine or the presence still of its alteration products, 

 a point to which attention was directed in the microscopic description of the 

 rocks. No. 1 is remarkable for its percentage of titanium, which is very 

 high, even when compared with that contained in the others, which are 

 themselves considerably above the average. All of the rocks contain a 

 large amount of water of hydration. The percentage of CO2 contained in 

 Nos. 1 and 2 indicates also that they are much altered. 



These analyses show that the rocks can not be classed with the typical 

 andesites. Should they be called andesites at all, they must be classed with 



