68 Geological Society of Dublin. 



thence as to the changes in progress, or hereafter to occur, to animal 

 and vegetable marine organization on our coasts ; to indicate by the 

 most ample and certain data the changes of soundings, of shoals, of 

 harbours, beaches and bars, which concern the mariner and the civil 

 engineer ; and to draw conclusions as to the relation and balance 

 between the wear of the land by detrital action, both meteorological 

 and tidal, and its replacement by forces of elevation, whether slowly 

 or convulsively. 



He mentioned this as one instance of experimental geology ; but 

 the direction in which he was at present anxious to have geology 

 advanced, by obtaining the aid of a co-operative movement in apply- 

 ing this method of investigation, was rather different. It had be- 

 come certain of late years that the crust of their globe, far from 

 being of that immoveable character which was popularly supposed, 

 was, in fact, one of the most unstable and changeable parts of crea- 

 tion, that there was nothing immutable upon it, but the very muta- 

 bility that marks and agitates it, was subject to almost continual 

 motion in both a vertical and a horizontal direction ; the latter re- 

 stilting, at uncertain intervals, principally from the cause which 

 produced earthquakes, the former occurring at occasional epochs 

 from the same cause ; and regularly recurring, in all probability, in 

 the form of annual and daily motions of expansion and contraction 

 in the earth's crust, due to alterations of temperature by changes of 

 season, and of day and night. To measure these motions appeared 

 of the very highest importance, at the present epoch, to the advance- 

 ment of geology. A communication from Sir William R. Hamilton, 

 which he (Mr. M.) had in his hand related to one of these pheno- 

 mena ; but to take matters in the order of their relative importance, 

 they should first consider these movements which related to the 

 earthquake oscillation of which he had spoken. 



It would be necessary, in order that the Society might understand 

 his meaning, and see more clearly the bearing of the motion as to 

 scientific co-operation, which he intended having the honour of lay- 

 ing before the Council at a subsequent period, to detain them with a 

 slight sketch of the movements due to forces of elevation and de- 

 pression which were known to be always taking place in the earth's 

 surface. 



That any portion of the earth's crust was absolutely permanent 

 as to level was uncertain ; that there were some portions which were 

 neither rising nor falling with respect to an assumed plane, at a fixed 

 distance from the earth's centre, was possible ; but that large tracts 

 were slowly rising, and that others were periodically caused to rise ; 

 again, that other large tracts were slowly sinking (for instance the 

 great coral region of the South Sea), and some suddenly depressed 

 (usually at periods of sudden neighbouring elevation), was certain. 

 The forces which produce these changes of level also give rise to 

 earthquakes. It was necessary for him to refer, very briefly, to some 

 particulars respecting the subject of earthquakes, on which he had 

 recently the honour to lay a paper before the Royal Irish Academy. 

 Every earthquake was in fact a succession, or a combination rather, 



