THE PRECAMBRIAN ROCKS OF THE CANTON QUADRANGLE I9 



The second type of area occupied by Grenville limestones, con- 

 trasted with the Hnear above described, is the irregular or intersti- 

 tial, if it may be so called. This is developed particularly in the 

 neighborhood of the large bodies of intrusive gneisses in the south- 

 central portion of the sheet, and in other parts where mechanical 

 deformation has been intense. In the vicinity of Pyrites, especially 

 south and east of that village, this large-scale interstitial character 

 of the limestone is well developed. Thus it is to be noted that the 

 granite gneiss and the gabbro-amphibolite are never brought into 

 actual juxtaposition by the intense deformation which affected the 

 region, but are always separated from each other by a continuous 

 limestone belt of varying width. This is sometimes noticeably con- 

 stricted where it is pinched in between closely adjoining resistant 

 masses of gabbro and granite, but it is never severed. An illustra- 

 tion of this is seen at the northern and western extremities of the 

 subcircular boss of granite east of Pyrites. At the latter point the 

 limestone, here but an extremely narrow strip, while it gives place 

 laterally to other members of the Grenville series, rusty gneisses 

 and schists, is nowhere mechanically interrupted through crustal 

 deformation. 



This feature, which is brought out by a consideration of the purely 

 areal relations of the crystalline limestones, is an excellent illustra- 

 tion of the relatively high degree of plasticity attainable by sucli 

 carbonate rocks during regional metamorphism under heavy cover. 

 The limestone has acted as a kind of buffer for the igneous gneisses, 

 and has been squeezed into the varying spaces between them and 

 accommodated itself with evident facility to an unusually irregular 

 distribution. 



The other limestone occurrences are small scattered patches, usu- 

 ally cut off abruptly in one or more directions as a result of intense 

 folding and subsequent tilting of the strata. North of Eddy tv:o 

 such patches are observed. While the boundaries drawn in these 

 two instances are merely intended to outline the areas characterized 

 by predominantly calcareous strata, and not the outcropping of defi- 

 nitely ascertainable structures, it so happens that the form of these 

 areas is suggestive of what is believed to be the primary tectonic 

 feature controlling the distribution of formations in this vicinity. 

 The lines suggest gentle anticlines and synclines, bevelled at a low 

 angle by the surface of erosion. It is not known that such low- 

 pitching open folds are actually present, but observation confirms 

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