. The Quarterly journal of the Geological Society of London. ll Lake, we observe how regular, andoften how minute, are the interleavings of gneiss, mica-slate, and darkcompact greenstone along the greater part of the Promontory and its 404 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [June 1 6, isles; but when we come to the south-east angle of this lake, these rocks(granite and gneiss being substituted for mica-slate) over an irregularspace of about 300 square miles are so mutually involved and inter-penetrated, and so intimately mixed up together, that it is impossibleto give any but the most gene
. The Quarterly journal of the Geological Society of London. ll Lake, we observe how regular, andoften how minute, are the interleavings of gneiss, mica-slate, and darkcompact greenstone along the greater part of the Promontory and its 404 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [June 1 6, isles; but when we come to the south-east angle of this lake, these rocks(granite and gneiss being substituted for mica-slate) over an irregularspace of about 300 square miles are so mutually involved and inter-penetrated, and so intimately mixed up together, that it is impossibleto give any but the most general account of their disposition, how-ever plainly seen and carefully observed on the spot. In some places(Portage Mouille, &c.) they are in narrow interleavings of no con-stant direction. In another (around Broken Road River) the granite,for large spaces, traverses dark greenstone in a thousand tortuousmasses, tongues, and slender veins. Fig. 2.—Sketch of a broken fragment of Greenstone (18 inches hy8) in Greenstone-conglomerate at Portage des Veins of granite and quartz, and shapeless or lenticular masses ofhornblende, rendered impure by a fine admixture of white quartz,are abundant in all these rocks ; but as such appearances are commonelsewhere, they are not here noticed in detail. Two veins of epidotictrap in granite, met with in an island near Portage Mouille, were soartificial in appearance that I sketched them. One of these is re-presented by fig. 3. The isolated needle of trap in fig. 3 is per-haps connected with the contiguous vein of that rock. Fig. 3.—Ground-plan of a portion of a Trap-vein in Granite nearPortage Mouille. Length 10 yards.
Size: 1835px × 1361px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1840, booksubjectgeology, bookyear1845
