ANNIVERSARY ADDRESS OF THE PRESIDENT. 6^ 



Further, the asserted passages between igneous and sedimentary 

 rocks rest at present on evidence which, I have already stated, we are 

 justified in putting out of court. They require confirmation, and 

 we know that many instances, once confidently asserted, have 

 broken down on strict examination*. Indeed, I may venture to 

 assert that, so far as my experience goes, the diflBciiltics at present 

 existing either are due to obliteration of the original structure by 

 subsequent mechanical or mineral change, or occur among the very 

 earliest rocks of which we are cognizant ; the latter are not only 

 likely to have undergone such changes, but also may have been 

 formed under circumstances which have never recurred in the 

 history of the earth. These, for the present, I put on one side, 

 hoping on a future occasion to return to them, and limit myself to 

 the great body of rocks which all admit to have solidified from a 

 state of fusion, and to those which (although field-evidence may be 

 wanting) we may reasonably believe, through their close structural 

 correspondence, to have been so formed. 



So much controversy, however, has existed as to the origin of 

 granite, that I shall venture a few additional remarks on this subject. 

 To me it appears to a very large extent a dispute about the two 

 sides of a shield. On the one hand, the phenomena exhibited b}' 

 granite masses intrusive into other rocks, {. e. sharply defined junctions, 

 contact-metamorphism, the sending off of dykes and veins which 

 gradually assume the structure of normal felsites, perhaps even of 

 rhy elites, justify us in asserting that granite cannot be separated 

 from the other plu tonic rocks such as syenite, diorite, and gabbro. 

 At the same time it is true that there are abnormalities incom- 

 patible (so far as we know) with the idea of dry fusion, and that 

 water is actually present in numerous minute cavities ; but the same 

 is true in some of the rocks above named. Further, I do not 

 suppose that any geologist at the present day would assert that 

 perfectly dry fusion is a common thing in nature, if, indeed, it ever 

 exists. Clouds of steam are discharged from the craters of volcanoes 

 and the surfaces of lava streams as they flow. The latter by parting 

 thus with their water will cool in a manner more analogous to that 

 of a furnace-product ; had the same material solidified deep in the 

 earth, a large portion of the water at any rate would not have been 



* With regard to the alleged transitions from igneous to sedimentarj' 

 rocks, Dr. Wadsworth, in his recent ' Litbological Studies ' (a copy of Tvhich 

 through the author's kindness reached me after the greater part of this address 

 was written), uses language which, though severe, is not unjustifiable (p. ]2). 

 After dwelling on the numerous cases where the asserted evidence of transition 

 has proved to be either negative or exactly opposed to the hypothesis, be con- 

 tinues : — " Practically, when the existence of these junctions has been shown, the 

 observers who had previously denied their evidence have always said, ' That is 

 not a typical locality ; we were not quite sure about that place, but if you will 

 go to such and such a locality,' indicating some new one, ' yovi will find an un- 

 doubted passage of sedimentary rock into eruptive forms.' When the new 

 locality is also examined and the statements are found to be erroneous, another 

 one is mentioned, and so on ; imtil one must demand hereafter of these observers 

 that they shall select some locality on which they shall be willing to fully and 

 finally stake their pet hypothesis, and abide by the evidence," 



