The greater part of the main road from Carillon to Grenville, a distance of thirteen miles on the northern banks of the Ottawa River, runs over the Calciferous sand rook of the Lower Silurian formation. In many places ihe surface of the rock is exposed, and beyond the village of Chatham, towards Grenville, and even in Chatham, for a short distance, the road consists of the solid limestone rock. As the surface of the rock is more or less rough or uneven, the road is an uncomfortable one to travel over in a wheeled vehicle. On driving over that part of the rock just near Chatham, a tremendous loud rumbling noise is occasioned by the stage, which is not heard, in other situation. This has been attributed to the presence of one or more large caverns situated beneath the road at this place: and, on making inquiry on the spot, I learnt that a prevalent opinion has long been entertained by the country people and many intelligent persons in the to neigbourhood, that a considerable cavern does exist in this part of the country in the place mentioned. On the many occasions that I have driven over this road, the loud rumbling noise has been invariably observed by my fellow travellers as well as by myself. Sotne-day an opening into the cavern may be discovered and the mystery solved. The main road is, elevated and is probably from seventy to ninety feet above the level of the Ottawa River.