Portland stone is an oolitic limestone laid down in the late Jurassic Period 135 million years ago. The rock was formed in a shallow tropical sea similar to areas of the Caribbean today. Minute grains of sand and shell were rolled across the sea floor, accumulating layer upon layer of calcium and creating tiny egg shaped structures known as ooliths, each one barely visible to the eye.
The fossil content of the rock beds that lie at the top of the Portland quarries is extremely high. Primarily consisting of bivalves (clams and oysters) and gastropods (marine snails), over time these abundant fossils have had their shells dissolved by acidic ground water, leaving behind voids in the stone with only the delicate outline of the fossil remaining.
The patterns that appear on the surfaces of Harrisson's structures are achieved by a direct rubbing on paper over the stone using a graphite wax stick. The varying folds and undulations combined with the pressure of the rubbing make direct reference to geological evolution and the myriad variety of long since vanished life forms.
Photography © Tom Harrisson
Photography © Tom Harrisson