A CONTRIBUTION TO THE GEOLOGY OF SOUTHERN MAINE 555 



All of the chemical ratios are essentially the same, as is of course 

 indicated by the fact that they fall into the same sub-rang. 

 The similarity is such as to indicate chemical relationship or 

 magmatic unity between the plutonic metamorphic rocks of the 

 older series and the younger diabases. This chemical and 

 "normative" likeness is the more striking in that it is not 

 accompanied by a mineralogical or model similarity. Any re- 

 calculation of the analyses of the older rocks in terms of the 

 minerals that are actually there brings about an appearance 

 of greater basicity than the normative relationship warrants. 

 In the hornblende schist the amount of hornblende is so great 

 as to give the rock every appearance of belonging among the 

 basic gabbros. When interpreted in terms of standard minerals 

 it becomes evident that the amount of hornblende has increased 

 at the expense of anorthite molecules and that the rock is 

 practically identical with the diabase. 



In Table XIV the analysis of all the Boothbay types analyzed 

 by us are repeated for comparison. It is evident that there 

 is a regular progression in chemical characters from I to IX, 

 and then a great difference when X is reached. It remains for 

 future investigation to show whether types intermediate between 

 IX and X are in existence, or whether X is really not a part of 

 this co-magmatic region. The distribution of peridotite and 

 allied dikes along the eastern parts of the United States is 

 suggestive of other than purely local relationships for this rock. 

 Leaving this dike aside we may thus sum up the chemical char- 

 acters of the region : the range of silica is moderate and its 

 amount intermediate, 49.00 to 67.59% being its extent. Alumina 

 is moderate in amount and does not show any definite serial 

 relation with other oxides. The ratios between lime, potash 

 and soda are variable, but in general as the basic end of the 

 series is approached, soda becomes in excess of potash, and lime 

 in excess of the sum of the alkalies. Iron and magnesia, as 

 well as lime, increase as the silica decreases; titanium is high 

 throughout. In the majority iron exceeds magnesia, but 

 magnesia increases relatively to iron as silica decreases. 



