Although the subject of this paper has already been discussed in detail, yet, as this has been done from a medical rather than from a geological point of view, it may be well that the chief facts of the case, the method of investigation followed, and the conclusions come to, should be brought before the Geological Society; for the Society will not fail to have an interest in noting what a practical bearing our science has on the health, as it has long been known to have on the wealth, of mankind.