The numerous excellent observations which have been made in recent years relative to the Palæozoic rocks in different countries in the Northern Hemisphere, require that we should now and again attempt to summarize the results obtained, and by that means bring before the mind more clearly any advance in our knowledge of past changes which has been made, as well as note those blanks which are still left for future investigations. In these considerations I cannot attempt to treat fully the various observations made, but I will endeavour to notice the chief results, or those points upon which new light seems to have been thrown.