Considering the prime importance attaching to the subject in almost every branch of geological inquiry, it is not a little remarkable that so little has hitherto been done towards obtaining precise measures of the actual waste of land-surfaces and comparing the rates at which the agents of destruction operate at the present time in different districts. Arrangements have indeed been made during recent years to observe systematically the results of marine erosion on our coast-lines, but concerning the far more important subject of subaërial erosion we have exceedingly few accurate data.