526 



OGILVIE 



and the direction of the cliff with respect to the strike has its 

 effect upon the form of the resulting headland. 



Petrology. 



It was the aim of the present investigation to deal only with 

 those rocks which are of igneous origin, whether metamorphic or 

 not. A considerable complex of schists and gneisses which ap- 

 pear to be of sedimentary origin was therefore left untouched. 

 Some of the types are distinctly doubtful in origin, and it is 

 quite possible that future research may add to the number of 

 igneous members. The probable sediments are clearly the oldest 

 components of the complex. By far the commonest of these 

 older* and doubtful rocks is a sandy mica schist, of decidedly 

 sedimentary aspect. Realizing the uncertainty of the evidence 

 of its sedimentary origin, and because of its very wide-spread 

 occurrence throughout the coast region of Maine, it was thought 

 that an analysis would be of interest. The analysis (Table II) 

 bears out the sedimentary hypothesis. The silica is higher than 

 in any of the igneous rocks of the region, though not excessive 

 for a granite. Lime, iron and magnesia are nearly equal in 

 amount, all being about 4%; the magnesia is relatively too high 

 for an ordinary granite; the sum of the alkalis is too low. 

 Though by no means conclusive the balance of chemical evidence 

 points towards a sedimentary origin; the same is true of mi- 

 croscopic, and of field details. 



Table II. 



Duplicate Analyses of Mica Schist (Probably of Sedimentary Origin) from 



Spruce Point, Boothbay, Maine, by M. W. Adams. 



Si0 2 



71.28% 



71.60% 



A1 2 3 



12.17 



12.38 



Fe 2 3 



.62 



•53 



FeO 



3- 6 4 



3- 6 4 



MgO 



3-27 



3-3* 



CaO 



4.07 



3-95 



Na 2 



2.79 



2.46 



K 2 



1.86 



1.89 



H 2 + 



•3 1 



•3i 



H 2 0- 



.09 



.09 



co 2 



none 



none 



Ti0 2 



i-i5 



1.08 



P 2 O s 



.20 



.20 



Total 



101.77 



101.12 



