Geology

Carp Ridge Geology with Dave Forsyth – A Macnamara Field Naturalists’ Club field trip in October 2017 along a transect (cross-section) of the Carp Ridge, from 1 billion year old Precambrian Grenville Basement granitic gneiss and syenite to 480 million year old early Ordovician bio-sediments.

Map 1508A – Generalized Bedrock Geology, Ottawa-Hull – An excellent overview of the area’s underlying bedrock composition from the Geological Survey of Canada.  The Carp Hills are clearly visible as an island of Precambrian rock set in a sea of Paleozoic limestone.  The Hazeldean Fault runs on the edge of the Carp Hills along the Carp Road where the Precambrian rock was thrust up above the limestone, which is now overlaid with fertile Champlain Sea sediments.  The highest points on the ridge occur along this fault line, which runs northwest/southeast, causing most water on the ridge to drain to the northeast (to Dunrobin).  Also visible are pockets of more alkaline rock (marble) in the Carp Hills, which allow plants that prefer sweet soil to flourish in the normally acidic environment.

Map 1363A – Arnprior – This map from the Geological Survey of Canada shows the bedrock geology of the Carp Hills in more detail.

Geology of the Ottawa Area (PDF), A Geoheritage Project by Quentin Gall (2010) – The first five pages of this field trip provide a nice overview of Ottawa’s geology.  The Carp Ridge and its PreCambrian Shield composition are specifically mentioned.