It would thus appear that physical and geological science conspire in assigning a great antiquity to the earth, but not an unlimited antiquity. They agree in restricting the ages that have elapsed since the introduction of life within one hundred millions of years. I confess, however, that a consideration of the fact that all our geological measures of erosion and deposition seem to be based on cases which refer to what may be termed minimum action leads me to believe that the actual time will fall very far within this limit. For example, if we were to suppose an elevation of the land drained by the Mississippi even to a small amount, its cutting power would be vastly increased for a long time. The same effect would result from a subsidence and re-elevation, or from any cause increasing the amount of rainfall or deposition of snows in winter. Now we know that such things have occurred in the past, while we have no reason to believe that the amount of action was ever much less than at present. Similar considerations apply to nearly all our geological measures of time; and there has been a tendency to exaggerate these, as if geologists were entitled to demand unlimited time, and to stretch the doctrine of uniformity to the utmost. 6. During the whole time referred to by geology, the great laws both of inorganic and organic nature have been the same as at present. The evidence of light and darkness, of sunshine and shower, of summer and winter, and of all the known igneous and aqueous causes of change, extends back almost, and in some of these cases altogether, to the beginning of the Palaeozoic period. In like manner the animals and plants of the oldest rocks are constructed on the same physiological and anatomical principles with existing tribes, and they can be arranged in the same genera, orders, or classes, though specifically distinct. The revolutions of the globe have involved no change of the general laws of matter; and though it is possible that geology has carried us back to the time when the laws that regulate life began to operate, it does not show that they were less perfect than now, and it indicates no trace of the beginning of the inorganic laws. Geological changes have resulted not from the institution of new laws, but from new _dispositions_, under existing laws and general arrangements. There is every reason to believe that in the inorganic world these dispositions have required no new creative interpositions during the time to which geology refers, but merely the continued action of the properties bestowed on matter when first produced. In the organic world the case is different.