In this paper I have reduced the periods of their occurrence for the thirteen years past to astronomical time, in all instances where the hour on which the shocks occurred have been known with certainty, and, without attempting to combat any theory that has been advanced, or the suggestion of another relating to their origin, their history has been left as a record of facts, which will become useful when others of like character accompany them. Our record, in this State alone has reached a little more than one-tenth of the number on which M. Mallet has founded his theory of their origin, and which were drawn from all parts of the world, and although this may seem a large proportion for this district of country alone since 1850, it is not to be presumed that a greater frequency of shocks have occurred here than elsewhere, but that the same attention has not been bestowed in recording their occurrence in other countries where they are known to be much more frequent and severe than upon our coast. It might be asked why, if such unquestionable frequency occurs within the limits of this State we are not subject to momentary destruction from their effects; the answer to this is found in the preceding paragraph, from which cause it will be seen that our experience is more apparent than real, relatively, and farther still, we should find a much greater frequency of shocks, beyond all doubt, if the instruments for their registry in different parts of the State were more plentiful than at present. There is no good reason for the supposition that we are in more danger from these phenomena than upon the Atlantic border, for the reason that we are so far removed from the centers of immediate and violent volcanic action, that it would require dangerous tension of the imagination to place California within the range of those physical causes which are so conducive to violent, repeated, and destructive earthquakes. This State cannot be considered more subject to earthquakes than it is to volcanoes, relatively, and this is said too in the face of our own records relating to the former. We need have little fear from these disturbances so long as we are so far removed on either hand from the great centers, and even from the terminal points of those centers of volcanic disturbance, from the action of which such disastrous consequences have, and will again follow to their immediate districts.