193 THE CANADIAN NATURALIST. [^ ; >y 



east and west, seldom deviating more than 20° to the north or 

 south of these points. The following observations were made in 

 the neighbourhood of Eagle River, at points where the slates ap- 

 peared most regular: N. 83° E., dip 45° northward; N. 80° W., 

 dip 46° northward; N. 45° E., dip 34° north-westward. 



In the foregoing description an attempt has been made to 

 delineate with fidelity the most important features of the Huronian 

 formation as developed on Lake Superior. It is now proposed to 

 give a fair unstrained interpretation of the characters stamped 

 upon the rocks of that series. The fact of the Laurentian granite 

 being pierced, as above described, by Huronian rocks, and the fact 

 of their enclosing fragments of such granite, proves incontestably 

 that some of them are of eruptive origin, and of later age than the 

 Laurentian series. The enclosure of the huge sharply angular 

 fragments of granite in the very basic greenstone, above described, 

 stands in intimate connection with the enclosure of smaller and 

 contorted granite fragments in a matrix of similar chemical com- 

 position, but different (slaty) structure. The appearances visible 

 near Eagle River, of which figure G is an illustration, prove that 

 enclosed granitic fragments sometimes undergo modifications of 

 form through contact with certain Huronian rocks. In Foster 

 and Whitney's Lake Superior Report (Part II., pp. 44 and 45), 

 analogous phenomena are described, but the exactly opposite con- 

 clusion is arrived at, viz., that the granite is in the form of veins, 

 and is the newest rock. There would seem to be only the two methods 

 of explaining the facts described : either the granite forms veins 

 penetrating the schistose greenstones, in which case the latter are 

 the oldest rocks, or it is in the form of contorted fragments, in 

 which case the enclosing rocks must be of eruptive origin. The 

 fact that the granitic fragments do not cut but run parallel with 

 the slates which enclose them, is the strongest argument against con- 

 sidering them to be veins. The supposition that they are long drawn 

 and contorted fragments seems to be most in harmony with the 

 facts stated, and with what is known as to the relative ages of the 

 Laurentian and Huronian rocks. The true explanation most 

 likely is, that the basic greenstone, after enveloping the granitic 

 fragments, continued for some time in motion, and, previous to 

 solidification, softened and rendered plastic the fragments, which 

 then became drawn out in the direction of the flow of the igneous 

 mass, and forced to accompany its sinuosities, and that the motion 

 of the fluid mass previous to and during solidification developed in 



