72 Geological Society : — 



4. " On the Obermittweida Conglomerate : its Composition and 

 Alteration." By Prof. T. G. Bonney, D.Sc, LL.D., F.lt.S., F.G.S. 



The Author is indebted to Professor Hughes for the opportunity 

 of examining a fine scries of specimens of this rock, collected by the 

 latter. The pebbles vary from well-rounded to subangular, some 

 of the smaller fragments occasionally being practically unworn. 

 The matrix is sometimes granular to the unaided eye, sometimes 

 very fine. The whole mass has evidently been subjected to con- 

 siderable pressure. 



The associated gneiss is a moderately coarse gneiss, containing 

 two micas and garnet. It has a general resemblance to rocks which, 

 in the Alps, appear to occur about or rather below the middle 

 of the crystalline series. 



The fragments consist of various kinds of rocks. Those examined 

 microscopically are referred to granitoid rock (3 varieties), mica- 

 schist, quartz-schist, quartzite, halleflinta (?). 



The matrix is almost wholly composed of quartz and mica (two 

 species, but mostly brown) with some felspar. The materials appear 

 to have undergone a certain amount of metamorphism, by augmen- 

 tation of the original fragments, and to some extent by development 

 of new minerals. The author is of opinion that the materials are 

 rather more altered than is usual in Palaeozoic greywackes and con- 

 glomerates, but that the comparatively small amount of alteration, 

 and the character of the included fragments, render it highly im- 

 probable that the conglomerate is in stratigraphical sequence with 

 the above-described gneiss, or with any similar series of rocks ; and 

 so, if Archaean, it must belong to one of the latest epochs in that 

 period. 



5. " Notes on a part of the Huronian Series in the neighbourhood 

 of Sudbury (Canada)." By Prof. T. G. Bonney, D.Sc, LL.D., F.U.S., 

 F.G.S. 



The specimens noticed by the Author were in part collected by 

 him in the summer of 1884, when the Canada Pacific Railway was 

 in process of construction, and in part subsequently supplied to him by 

 the kindness of Dr. Solwyn, Director-General of the Geological 

 Survey of Canada. 



The eastern edge of the district assigned to the Huronian consists 

 of rocks, which may possibly be part of the Laurentian series modi- 

 fied by pressure. But after crossing a belt of these, barely a mile 

 wide, there is no further room for doubt. All the rocks for many 

 miles are distinctly fragmental, except certain intrusive diabases or 

 diorites. These fragmental rocks are grits, conglomerates and breccias, 

 which are described as far as about 2 miles wesl of Sudbury. The 

 included fragments in these rocks appear to have undergone some 

 alterations subsequent to consolidation: these are described. In 

 some cases the changes appear to be anterior to the formation of the 

 fragments. The matrix also has undergone some change, chiefly 

 the enlargement of quartz grains, and the development or comple- 

 tion of mica-flakes, as in the Obermittweida rock. 



The Author gave some notes on other specimens collected by him 



