On the age of these deposits it is useless at present to speculate. All that we know for certain is, that geologically speaking, they are recent; but whether it is five hundred, or five thousand, or fifty thousand years since the present site of Mountain Lake was on a level with the ocean, our present data do not enable us to form an opinion. All that the facts prove is that this portion of the continent is being gradually raised en masse.
From observations I have made on the main range of the Sierra, I am inclined to think that this process of gradual elevation is not confined to the land bordering the sea coast, but extends far into the interior. The undisturbed position of the post tertiary strata on the western slope of the Sierra, would indicate that the same process of gradual elevation must have been going on for hundreds of thousands of years, so that the original beach of the earlier post tertiary ocean is now at an elevation of four or five thousand feet above the present level of the sea. Should subsequent observations confirm the truth of this supposition, this country would afford a more striking example of the action of existing causes in modifying the surface of the earth, than is to be found in any other portion of the globe. It is desirable that some means should be taken to ascertain and record accurately the present relative level of the sea and land, as, after a few years, such a determination might furnish some very useful geological data. I have no doubt that it will be found that every shock of an earthquake is accompanied by an elevation of the land.
San Francisco, July 6th, 1863.
Regular Meeting, July 20th, 1863.
Dr. Ayres in the Chair.
Twelve members present.
J. B. Bayerque, Esq., was elected a Life Member.
Donation to the Cabinet: A number of birds and quadrupeds were deposited by Mr. W. W. Holder.