178 



rites and gneisses is all the more singular, since the two series 

 are everywhere as distinct petrologically as mineralogically. 

 Reference to the map will show that there is scarcely a point 

 where the amygdaloid is in contact with the diorites, either 

 stratified or unstratified. The fact that the diorites, partially 

 inter stratified with the petrosilex (our typical Huronian terrane) , 

 are found over this entire region, being in a certain sense coex- 

 tensive with the Huronian series, and are characterized by a 

 prevailing N.E.-S.W. strike and north-westerly dip, indicat- 

 ing a general independence of the present configuration of the 

 surface ; while the amygdaloid is confined to the margins of 

 basins which have very clearly been eroded from the upturned 

 and extravasated dioritic and other Huronian terranes, — is satis- 

 factory proof of the entire distinctness and separateness of the 

 two formations. 



The amygdaloid can be connected with the diorites in only 

 one way, and that is by the bond of derivation ; the two 

 formations are probably genetically related. The chemical 

 decay and disintegration in ancient times of the basic division 

 of the Huronian series must have yielded sediments similar to 

 those required for the formation of the amygdaloids. The 

 feldspar of the diorites was extensively kaolinized, and the 

 hornblendic material changed so as to have the chemical aspect 

 of chlorite ; species of alteration to which, as geologists are aware, 

 these minerals have been subject in all ages, when exposed to 

 the action of atmospheric agents. Still clearer is the derivation 

 of the breccias from the acidic division of the Huronian series. 

 The disintegration in this case was more mechanical than 

 chemical ; still there is evidence that much feldspar was 

 changed to kaolin and to a hydrous aluminous silicate ap- 

 proaching pinite. Thus from the ruins of the Huronian series 

 was formed a second twofold formation ; the primary divisions 

 of which, although presenting important chemical differences 

 when compared with the parent terranes in the ancient system, 

 may yet, like them, be distinguished as basic and acidic. It is 

 here easy to see how this most fundamental distinction among 



