Rock Texture & Pattern at Dog’s Bay

The rocks at Dog’s Bay in Connemara, Ireland, are part of the Galway Batholith. In particular they are composed of the Errisbeg Townland Granite riven by faults and many dikes containing other younger intrusive igneous rocks. The juxtaposition of the different rock types is a phenomenon marked by contrasting, colours, textures, and patterns. The whole rocky terrain has been levelled off and smoothed by ice sheets and reflects many glaciation features.

Feely, M. Leake, B.E., Baxter, S. Hunt, J. and Mohr, P. A Geological Guide to the Granites of the Galway Batholith, Connemara, western Ireland.Geological Survey of Ireland, 2006.

Volcanic Tuff near Louisbourg Lighthouse – Part 3

Rock colour, pattern, and texture in the Main-a-Dieu sequence on Cape Breton

On a whole range of scales, there are variations to the simple layering of the tuff (which is made of volcanic ash) and constitutes swathes of faintly striped and banded rock on the shoreline at Louisbourg on Cape Breton Island in Nova Scotia. Subsequent to the deposition and consolidation of the volcanic ash into tuff rock, the build-up of great pressures from earth movements at different times during geological history has caused both minor and major fractures in the rock. Small cracks sometimes filled up with dissolved minerals that crystallised to form veins of contrasting coloured material. In other places, intrusive molten lava squeezed its way into weak areas between or across the layers forming large-scale dikes. The igneous rock type of the dikes may be a greenish colour, and often cracks upon weathering in a characteristic way giving it distinct fracture patterns that are not present in the tuff.

[We stayed at the most excellent Louisbourg Harbour Inn while we explored this part of Cape Breton Island.]

Rock colour, pattern, and texture in the Main-a-Dieu sequence on Cape Breton

Rock colour, pattern, and texture in the Main-a-Dieu sequence on Cape Breton

Rock colour, pattern, and texture in the Main-a-Dieu sequence on Cape Breton

Rock colour, pattern, and texture in Main-a-Dieu sequence volcanics near Louisbourg

Rock colour, pattern, and texture in the Main-a-Dieu sequence on Cape Breton