The area occupied by Lower Palæozoic rocks in Victoria is an extensive one, and is pretty equally divided between Ordovician and Silurian, the part occupied by Cambrian being small. According to Dr. A. R. C. Selwyn, formerly Director of the Geological Survey of the Colony, the total area amounts to somewhere about 30,000 square miles in extent, and although in this estimate he included all areas occupied by these rocks provided the cover was not more than. 350 feet in thickness, it will still leave us with a large extent of country over which graptolites may be found.