Geology At Tucker House

Tucker House and Clarence-Rockland sit on the low, rolling plain of the St. Lawrence Lowland.  To the north are the Gatineau Hills, remnants of the once-mighty Laurentian Mountains, part of the more extensive Canadian Shield that contains much of Canada's mineral wealth.  On the west lies a southward elongation of the Shield called the Frontenac Arch, and to the south stand the Adirondack Mountains.
 
The St. Lawrence lowland has an ancient history.  About 500 million years ago, in the early Paleozoic Era, it was covered by a vast ocean.  Sheet-like layers of limestone, sandstone and shale were deposited on top of the rocks of the Shield, on the bottom of the sea. These layers contained the remains of creatures that lived in those warm, then-tropical waters.  Later, earth movements ("tectonism" in geological language) split the earth's crust and caused it to drop downwards.  This "blockfaulting" protected the sediments of the Lowland from being removed by erosion during the rest of Paleozoic, Mesozoic and Cenozoic time.
 
The last major geological event in the region, very recent in terms of geological time, was the Pleistocene glaciation, consisting of repeated invasions of massive continental glaciers from the north.  The most recent advance of the ice, known as the Wisconsin glaciation,  began about 120,000 years ago and ended about 12,000 years ago.  This moving ice sheet gouged off, ground up and carried the tops of the Laurentian Mountains -  what was left of them after millions of years of erosion - onto the St. Lawrence Lowland, leaving only the rounded hills that we see today in Gatineau Park.
 
As the ice finally retreated, marine waters of the Champlain Sea invaded the Lowland from the east, depositing sand, clay and fossil clams, barnacles, and even whale-bones. The sea withdrew gradually, reaching its present position by about 9,000 years ago as the land rebounded (geologists call it "isostatic adjustment") from the weight of about two kilometres of ice.
 
On the Tucker House property billion year old Precambrian boulders of granite and gneiss from the Shield are scattered about In the woods and fields, where they were dropped by the melting ice. One of the largest of these "glacial erratics", in the woods west of the white cottage, is about a metre in diameter and has a flat side produced as the moving ice dragged it over the exposed 450,000,000 year old Ordovician bedrock.  If you look carefully at the erratics, maybe with a magnifying glass, you may see the black minerals biotite, hornblende and pyroxene, and the white minerals muscovite, quartz and feldspar.  Muscovite has been mined from the Gatineau Hills for use in radio parts, and for windows in wood stoves.
 
The original Lower Paleozoic sedimentary rocks of the Late Ordovician Rockland Formation can still be seen, in the very quarries from which Stephen Tucker carried away wagon-loads of stone 135 years ago to build the foundations of the house and barn.  Some of the beds in the quarries and building foundations contain the fossilized remains of corals, brachiopods, crinoids and bryozoans that lived in the half-billion year old sea.  The Tucker House organic gardens are built on the layer of Leda Clay that was deposited in the post-glacial Champlain Sea, and the bricks used to build the house were made from this clay.
 
Under the gardens, green lawns and forests of Tucker House and in its quarries are records of the primordial history of the Ottawa Valley, a catalogue of millions of years of ancient oceans, primitive creatures, cataclysmic earth movements, continental glaciers and shallow inland seas.  Within these 32 acres one can catch glimpses of how this part of the world came to be.