Operation of the Teredo Navalis on colonial timber

In attempting to form an estimate of the cost of constructing and maintaining a range of wharves, whether along the sea-coast exposed to the action of salt water as at Hobart Town, or upon the banks of a river where fresh water can only operate upon them as at Launceston, one great element in the account will always be the relative duration of the materials which the engineer may have at his disposal; whether such materials be exposed to merely the common causes of decay, namely, the action of the air or the water, with the ordinary wear and tear of the structure of which they form a part, or to some local and peculiar action,—such as, in the case of timber, the destructive agency of the Teredo navalis and other worms.