350 Scientific Proceedings, Royal Dublin Society. 



Contact, for which I have proposed respectively the terms Meta- 

 pepsis and Paroptesis (see " Geology of Ireland," p. 175), and 

 Chemical change, called by King, of Gralway, Metliylosis, while for 

 a molecular change the American authorities use the term Para- 

 morphosis. At the present time it is not intended to refer to the 

 rocks of the latter classes, as these preliminary remarks refer 

 specially to the others. 



Paroptesis, or Contact metamorphism, must necessarily occur 

 at a different time from Metapepsis or Regional metamorphism, in 

 one and the same area ; and the former may have taken place be- 

 fore or after the latter ; or possibly there may have been two or 

 more periods during which one or other of the actions may have 

 been in force — thus, for instance, in a region there may have been 

 first, in places, Paroptesis, which was succeeded by Metapepsis; 

 while subsequently, in places, there was a newer Paroptesic action, 

 or newer Metapepsis. The present state of metamorphism of some 

 of these older Canadian rocks would seem to suggest that they had 

 been subjected to a succession of alterations due to both of these 

 kinds of metamorphism. 



The S. E. of Ireland is an instructive area ; as on both sides 

 of the granite protrusion of the Leinster range there are bands 

 of Paroptesic rocks. Those to the westward of the granite ridge 

 have not been again altered (except some hereafter to be men- 

 tioned), while those eastward of the ridge have all experienced 

 a second change, due to Metapepsis, which invades nearly all the 

 Lower Palaeozoic rocks of these portions of the counties of Dublin, 

 Wicklow, and Wexford. 



Thus, as a general rule, to the westward of the granite ridge 

 there is a band of " baked " rocks, due to Paroptesis ; while east- 

 ward of the ridge there is a band of typical gneiss and schist [due, 

 first, to Paroptesis, and subsequently to Metapepsis], outside which 

 are more or less metamorphic rocks [due to the subsequent meta- 

 pepsis]. The metapepsic action seems to have been most intense 

 in certain oblique westerly and easterly lines, so that if we traverse 

 the region from north to south we will alternately pass over meta- 

 morphic and sub-metamorphic rocks ; that is if we ignore a subse- 

 quent action now to be mentioned. 



In this region, besides the intrusions of the normal Leinster 

 granite (Cambro-Silurian age?), there were also newer intrusions 



