The Lower Cambrian Rocks.
“But perhaps the most interesting rocks known in the Barren Lands are those which are regarded by the Canadian Geological Survey as being of Lower Cambrian age, and which are very similar in character to the Nipigon or Keewenawan rocks of Lake Superior.
A Survivor of Sir John Richardson’s Arctic Expedition wearing the Arctic Medal given him for that Expedition.
“In the exploration of this country recently made these rocks were first met with about the centre of the west shore of Dubawnt lake, whence they were found to extend north-northeastward for one hundred and twenty-five miles to the forks of Dubawnt river. From this point they were traced eastward for one hundred and seventy-five miles to the outlet of Baker lake, at which point they veered off to the south. Towards the west this series probably extends a long distance up the valley of Thelon river, and may perhaps cross the low watershed and connect with similar beds on the shores of Great Slave lake.
“The basal portion of this series is here represented by reddish thick-bedded sandstones and conglomerates, which are comparatively unaltered and undisturbed over large areas. In some places, as on the islands near the northwest shore of Dubawnt lake, they dip regularly at a moderate angle. The pebbles in the conglomerates are well rounded and water-worn, and consist almost entirely of white clastic quartzites like that of Marble island (Huronian) beds. The occurrence of quartzite pebbles, to the almost total exclusion of pebbles of Laurentian or other rocks, would indicate that these Cambrian strata were deposited off a shore composed very largely of Huronian quartzites. The sandstones and conglomerates are cut by dykes and masses of both acid and basic eruptive rocks. The acid eruptions were first met with on a hill of red quartz-porphyry at Teall point, on the west shore of Dubawnt lake. A similar massive quartz-porphyry forms a heavy east and west dyke, some distance farther north on the shore of the same lake, and in the vicinity of the dyke the surrounding conglomerate is very hardened, so that it breaks indifferently through the matrix or through the pebbles.
“Towards the north end of Dubawnt lake the orthoclase in the rock is replaced by plagioclase, the porphyry thus becoming a porphyryte. This porphyry is largely developed, and seems to underlie a large tract of country, along Dubawnt river between Lady Marjorie lake and the Forks, and again it was found on the island towards the east end of Baker lake.
“Dark-green basic eruptions, chiefly, or perhaps exclusively, in the form of dykes, are extensively developed throughout the area covered by the rocks of the Cambrian system. On Dubawnt lake and on Dubawnt river near the Forks, most of these dykes
Are of Typical Diabase,
with interlocking lath-shaped crystals of plagioclase, between which are crystals, or crystalline masses of augite, often altered to chlorite.