394 THE PENOKEE IRON BEARING SERIES. 



the belt under discussion — probably as much as 2,000 feet thick — is in 

 part a fragmental and in part a nonfragmental sediment. Such deposits 

 are rather unusual in the Iron-bearing series in the Northwestern states. 

 Layers of mingled fragmental and nonfragmental material are jjresent 

 in certain localities in the Animikie and other series. According to 

 the ideas generally accepted among geologists nonfragmental sediments 

 originate under water of considerable depth which is coraparativel}' quiet. 

 How, then, does it occur that a thick belt of sediment contains both frag- 

 mental and nonfragmental material? This singular occurrence can be 

 explained by supposing unusual conditions to have prevailed at the time 

 of the formation of the belt. In the present place it will only be remarked 

 that it is deemed probable that the exceptional conditions were due to 

 eruptive activity in the immediate neighborhood. This probalile comiec- 

 tion between the mingled fragmental and nonfragmental sediments of the 

 belt under consideration and the eruptives of the greenstone and greenstone- 

 conglomerate areas will be more fully considered in another place. 



Coarseh/ fragmental rocks. — In the north part of Sec. 23 and the noi-th- 

 east part of Sec. 24, T. 47 N., R. 43 W., Micliigan, and in Sec. 28, T. 47 

 N., R. 42 W., Michigan, occur excejitional phases of rock, recomposed 

 granites, conglomerates, and chert-breccias, niingled with which are chert)' 

 and ferro-dolomitic quartzites. Recomposed granites occur at each of the 

 places mentioned. In the field these rocks so closely resemble the original 

 granite that they are with difficulty separated from ii. Only in thin section 

 is the fundamental difference appreciated. The granites to the south have 

 a structure characteristic of a thoroughly crystalline rock. Thin sections 

 of the recomposed granite, upon the other hand, show it to consist of 

 fragments of various sizes, which are packed very closel}- together. 

 Most of these fragments are complex, and if a section chances to be cut 

 from a. single one of them it is, of course, precisely like a section from an 

 ordinar)' granite. A set of sections, however, is sure to disclose the fact 

 tliat tlicse rocks are clastic, there being always discoverable thin films and 

 small areas of finer material filling the spaces between the larger fragments 

 and cementing them together. This cementing material is generally finely 

 (MNstallinc silica and a, carbonate whicli is usuallv ferriferous. Tlicse 



