19. Pinhey's Point
Ordovician rock and Quaternary sediments at an historic homestead
Pinhey's Point
Pinhey Point Rd. off 6th Line Rd. Kanata, Ont.
Precambrian erratic boulder on Rockcliffe Formation sandstone, Pinhey's Point.
Photo by J. Aylsworth
The Pinhey's Point Historic Site is underlain by Ordovician-age (about 470 Million years old) bedrock, and covered with a thin veneer of Pleistocene-age glacial and marine deposits, and more recent (during the last 8000 years) soil and sediment related to the establishment of the Ottawa River.
The Ordovician bedrock in the Pinhey's Point area consists of fine-grained sandstone (Rockcliffe Formation), and slightly younger limestone that is part of the Ottawa Group. These two rock units are locally separated by a northwest-trending fault. The trace of this fault forms the embankment that slopes down to the Ottawa River immediately beside Pinhey's house and the barn.
Cropping out along the Ottawa River shoreline on the Pinhey's Point Historic Site are horizontal beds of the Rockcliffe Formation sandstone. In most of the exposures, thin beds of grey-green, fine-grained sandstone display ripples that were formed by waves and currents that moved the sand along an ancient shallow sea floor during the Ordovician. You can also see, in the rippled sandstone, horizontal burrows which were formed by ancient organisms as they moved along the rippled sands, perhaps as they were feeding on nutrients in the unconsolidated sediment. These horizontal burrows are called trace fossils, as they are not fossils but structures developed by the activity of the organisms living in the shallow marine environment during the Ordovician Period. Thicker sandstone beds display cross bedding.
The Ottawa Group limestone is not as well exposed as the Rockcliffe Formation sandstone. However, one place that you can see it is in the house, where the limestone forms part of Mrs. Pinhey's kitchen floor. You can also see the local limestone in the stone walls of the buildings. These limestone building stones were locally quarried, then crudely-shaped and bush hammered into platy and rectangular blocks. A close look at the limestone blocks in the walls will reveal fossil fragments, rounded mud pieces, thin bedding, jagged near-horizontal lines (stylolites), and some ripples and small cross beds.
Scattered around Pinhey's Point Historic Site are erratics - rounded boulders that were eroded and carried to this site by glacial ice during the last Ice Age. Most are Precambrian igneous and metamorphic rocks and were likely eroded from the Gatineau hills. Some of these boulders have been used as borders beside the walks and roads. The stony-sandy soil in the surrounding fields is till, another deposit of the glaciers.