GLACIAL ORIGIN OF HURON I AN ROCKS 



463 



The conglomerate is remarkable for its heterogeneous appearance. 

 Not only are the bowlders of a great variety of types but in many cases 

 they show no evidence of arrangement according to size. Frequently 

 one finds bowlders a foot in diameter scattered irregularly and sparsely 

 through an aphanitic matrix of shale or graywacke, thus simulating 

 glacial deposits. In other cases there are thick beds of shale quite free 

 from such erratics. There are also beds of bowlders of nearly equal 

 size packed close together and with but little of fine-grained matrix, 



Fig. 4. — Huronian conglomerate, Buffalo Mine, Cobalt, Ont. A weathered sur- 

 face of coarse facies. 



as in an ordinary water accumulation of coarse gravel. In some 

 instances the aphanitic beds are distinctly laminated as in ordinary 

 water-laid clay, while again similar material forms a compact rock 

 lacking in well-developed bedding planes. 



As a general rule the large bowlders are well rounded or sub- 

 angular; but there are occasional streaks containing markedly 

 angular fragments. Dr. Coleman found some bowlders at Cobalt 

 which show striae and concaved surfaces. 



The matrix of the conglomerate, which is often graywacke and less 

 often shale, contains numerous angular particles of quartz, feldspar, 

 chert, and felsites. Particles of such shape are very characteristic 

 of, though they are by no means found only in, glacial debris. 



