^6 Proceedings of the Royal Irhh Academy. 



Indeed tte great difficulty Trhich. meets the corLScientious writer of 

 ffistory, at every step, is that of placing the reader in a position to 

 realize as fully as possible the conditions under which the erents he 

 narrates have taken place, and that for the particular period he may 

 be treating of. Even correct maps can only represent the present state 

 of the country or ground considered, since accurate surveys may be 

 said to date from the nineteenth century only. As to the geographical 

 delineation of countries previously to that time, one has only to examine 

 the maps of the eighteenth and seventeenth centuries to become avrare 

 of their insufficiencies and defects however valuable they may have 

 been at the time or may be still historically. As to restorations, the 

 remarks of Sir Charles Lyell in this respect are well worthy of citation. 

 " The difficulty," he says, "or rather the impossibility of restoring the 

 geography of the globe, as it may have existed at any former period, 

 especially a remote one, consists in this, that one can only point out 

 where part of the sea has been turned into land, and we are almost 

 always unable to determine what land may have become sea " (Lyell's 

 "Principles of Geology," vol. i., p. 255). 



As regards Great Britain and Ireland the splendid maps of the 

 Ordnance Sirrvey give us the correct representation of these countries 

 as they are at the present period, and furnish therefore a thoroughly 

 complete and reliable standard by which to judge of the changes that 

 time may bring, or by which to work out what may have been the 

 geography of these countries in former times. 



It might be supposed that but few changes can have taken place 

 in the outline or general character of these islands during historical 

 time, and that any such changes, if of any magnitude, would be found 

 recorded in some document or historical work. That many records of 

 such changes exist is certaia, but that all have been noticed or recorded 

 is very doubtful. The changes attributable to atmospheric erosion 

 during historic times, are probably on the whole not very great, and 

 have been more or less approximatively estimated by geologists. Those, 

 however, which have been due to the action of the ocean on the coast 

 lines are in certain respects more important and more easily observable. 

 Few great storms from the west, north-west or south-west fail to leave 

 their mark on the coasts somewhere or other; and the steady continuous 

 beat of the Atlantic waves on the rocky headlands and coast lines 

 works theu' disiategration and removal, slowly it may be, but most 

 effectually. As an example of this action on the east coast of Ireland 

 may be pointed out the coast line between Killiney and Bray, as also 

 that between Bray Head and Greystones, along which considerable 



