A microscopic study of sandstones of Old Red Sandstone and Carboniferous ages along a part of the North Crop of the South Wales coalfield reveals that the rocks are extensively fractured. The fractures occur in the quartz grains and are often filled with bubble-like inclusions. These planes of inclusion were studied in specimens over a wide area, and are related to the directions of faulting and jointing. The consistency in trend between the macro and microstructures suggests a homogeneity of the deforming stresses.

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