126 3 MORLEY E. WILSON 
clastic sediments of this character, the pebbles and bowlders are 
commonly subangular or angular in shape though round fragments 
are also present. 
Greywacke and argillite—The basal conglomerate of the Cobalt 
series commonly passes gradually upward by the loss of its pebbles 
and bowlders into greywacke and argillite. This greywacke was 
originally a ferromagnesian sand and the argillite a ferromagnesian 
mud, both of which are now, however, very firmly cemented, the 
Fic. 1.—Photomicrograph of conglomerate matrix. Ordinary light. X20 
argillite resembling a slate but differing from a slate in possessing 
no slaty cleavage. The greywacke and argillite, like the other 
members of the Cobalt series, vary greatly, and here and there 
contain beds of arkose, masses of conglomerate, and, in some 
places, single isolated bowlders. In a few places the greywacke is 
unstratified, but as a rule both it and the argillite are uniformly 
bedded. The microscopic examination of the greywacke shows 
it to consist of fragments of quartz, feldspar, basalt, andesite, and 
other ferromagnesian rocks along with an abundance of chlorite. 
