THE LOWER HURONIAN. 311 



The proportion of the different kinds of pebbles varies greatly, and 

 consequently we find conglomerates of very different chemical and physical 

 aspects. The dependence of the character of the conglomerate on the 

 petrographic natnre of the adjacent rocks from which it has been derived is 

 well illnstrated as we follow northward the line of contact between the 

 granite of Saganaga Lake and Ogishke conglomerate on Cache Bay of 

 Sao-anag-a Lake, where we ffet the Offishke conglomerate in contact with 

 the Ely greenstone, which has been cnt by numerous dikes of the granite 

 of Saganaga Lake. As we go in this direction we find that the basal 

 conglomerate contains occasionally fragments of greenstone, and these 

 become more and more numerous, the granite appearing in proportionally 

 smaller quantity as the area in which the greenstone occurs is approached. 

 Finall}^, when we get well within the area in which the greenstone occurs, 

 the conglomerate is made up chiefly of greenstone fragments, the matrix 

 likewise being detrital material from the greenstone with onlj- an occasional 

 granite pebble, derived probably from the granite dikes which traverse 

 the greenstone or possibly transported from the main granite area. The 

 changeable character of the basal conglomerate within a very limited area, 

 its character depending on the petrographic nature of the surrounding 

 rocks, is also seen here, as above described, and shows the iincertainty of 

 correlations which depend on the similarity of the lithologic character of 

 sedimentary deposits occurring in widely separated areas. The differ- 

 ences in the Ogislike conglomerate at various localities is clearly due to 

 the varying character of the immediately adjacent rocks from which the 

 conglomerates have been derived. This is shown at a number of places. 

 Thus in some conglomerates all of the pebbles are greenstone, and the 

 matrix is likewise made up of the dust from these greenstones, so that the 

 resulting rock is green, with pebbles showing various textures, such as occur 

 in basic rocks. Jasper occurs in numerous fragments in these rocks, and 

 their brilliant color offers a very striking contrast to the usual monotonous 

 green of the conglomerates. Here and there a pebble or bowlder of granite 

 will appear, and again there may be an approximately even mixture of 

 pebbles of granite and greenstone. In other places the fragments of granite 

 are present in such quantity that they are the predominant bowlders. In 

 such places the matrix likewise is found to have changed from the green of 

 the greenstone conglomerates to the gray or pinkish color characteristic of 



