STRUCTURAL GEOLOGY. 39 



Characteristic elements of the alkaline magma.] 



and all relations are to be seen within a small compass, affording better opportunity 

 for study. At the same time the original clastic rock is one of marked peculiarities, 

 different from most of the elastics of the Archean, in the possession of peculiar 

 augites and feldspars which are probably of the nature of volcanic ejecta. This 

 peculiarity is perpetuated in the resultant granite, which is a peculiar one, different 

 from most of the granites of the state. 



(3). Source of the characteristic elements of thealkaline magma. If it be true that 

 the granites and other alkaline-acid igneous rocks of the Archean are the product of 

 the aquo-igneous fusion of the fragmentals of the Archean itself, it becomes necessary 

 to search for the cause of their characteristic chemical composition in the nature of 

 those fragmentals. In a previous paragraph attention was called to the essential 

 chemical differences between the alkaline magma and the ferro-magnesian. They 

 consist in the presence, in the alkaline, of a noteworthy per cent of the alkalies, and 

 of a large per cent of silica, a fact which precludes the derivation of the alkaline 

 magma from the ferro-magnesian by any process of lixiviation, or "fermentation," 

 or differentiation. It seems to be required, therefore, to find a satisfactory explanation 

 of the existence in the fragmentals of the additional elements in excess of those 

 amounts of the same which occur in the ferro-magnesian magma. 



The nature and origin of those fragmentals immediately come into consid- 

 eration. They are largely of volcanic origin, and contained originally not only the 

 augite crystals from which has been derived their predominant hornblende, but also 

 the olivine, the menaccanite and the soda-lime feldspars which characterize the 

 ferro-magnesian rocks of the Kawishiwin. These original minerals were subjected 

 to the manifold disintegration and final destruction which is incidental to oceanic 

 action. Their soluble parts went into the oceanic waters, and their insoluble consti- 

 tuted the debris which went, so far as it was able, to form the sedimentary strata of 

 the Archean. The ocean's waters must have been frequently heated by volcanic 

 ejections, and locally charged with the gases and acids which characterize volcanic 

 products. Such ejections would give rise to soluble chlorides and sulphates of the 

 alkaline bases and of iron and would thus be able to take up silica from the decay 

 of the rocks, and these substances would be distributed by currents to all parts of 

 the globe. These salts would vary from time to time, and from place to place, some- 

 times reaching saturation. Precipitation would take place when the balance of their 

 saturation point was broken by physical changes, such as lowering of temperature or 

 an influx of currents bearing elements that caused a change in their chemical com- 

 binations. All these physical irregularities must have been due, in this early volcanic 

 age, primarily to the movements set on foot by volcanic activity. It is impossible 

 to state, and even to conceive, of the millions of fluctuating conditions in that 



