Some Examples of detailed Structure in Early Pre-Cambrian Rocks of Canada

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Abstract
The geologist who is assisting a mining company in the search for ore in Pre-Cambrian rocks observes, in the course of mapping and interpreting the geological structure, many details of scientific as well as economic interest. The following paper deals with some of these observations, concentrating on typical structural forms as shown by several examples in northern Ontario and Quebec, and on factors relating to the form of certain intrusions. The field evidence for the features described below comes from three sources: first, from detailed surface mapping; secondly, from the mapping of underground workings in mines; and thirdly, from the “logging” and plotting of geology from diamond drill cores, thousands of feet of which are obtained annually at all the larger mines and on many properties under preliminary surface development. Outcrops are fairly abundant except in areas where post-glacial lakes deposited a thick layer of varved clay or sand. In most places weathering has barely penetrated the smooth and polished surface produced by the Pleistocene ice sheet, so that details of structure are very clearly shown. An attempt is made below to analyse these structural features of deeply eroded rocks, to deduce the stresses under which they were formed, and to correlate them with the features and stresses prevalent in the upper part of a folded section of the earth's crust as seen in younger mountain systems formed in later epochs. All the rocks mentioned in the present discussion are older Pre-Cambrian (prior to the ep-Archæozoic interval) with the exception

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