EEUPTIVE AXI) SEDDIEXTAEY AGENCIES DISCUSSED. 23 



o-eoloo-ist be placed upon this old volcivnic ground worn down to its roots, 

 its rocks altered or Tnetaniorphosed, its remnants of mingled lava flows, eject- 

 amenta, and marine deposits, and let him be asked to give its history. If he 

 were educated in the prevailing views current in American geological liter- 

 ature, it is probable that he would declare that this was an old chemical 

 or sedimentary deposit, which had been buried thousands on thousands of 

 feet deep under other sedimentary deposits, and in which, owing to the 

 inclosed moisture and the rise of the internal heat, an aqueo-igneous solu- 

 tion had set in, rendering the formation plastic. He would also say, that 

 owing to the generated gases and pressure, the lower portions of the deposit 

 had been forced into the upper ones, and every gradation had been produced 

 between the normal sedimentary rock and eruptive forms, which pass by 

 insensible gradations into each other. How easy and simple would this 

 explanation be! — nothing could be shown which the authors of such theories 

 could not explain. But how false in our supposed case such an ex2)lanation 

 would be. If we add to our supposed volcanoes massive eruptions, with or 

 without fragmental ejections (explosive action), shall we not have the same 

 petrographical featm-es that now exist in regions of the older crystalline 

 rocks ? — and is the explanation generally adopted for them any more 

 accurate ? 



The intermingling of eruptive and detrital deposits here supposed is 

 described in almost ever}^ work on volcanic action, and it has been clearly 

 shown, in many of these districts of older crystalline rocks, that the series 

 of events here indicated has been very common. 



That sedimentation has done its part the writer believe.s, and he has not 

 the slightest wish to belittle its importance ; but that it has done everything 

 he does not believe. Whether any of the first-cooled masses may ever be 

 found, is a problem for the future ; but that we have to do with material 

 that was fluid before sedimentation began, we consider is clearly established. 



To volcanic phenomena, whether explosive or massive, and to the as- 

 sociated water action, appear to be due the phenomena of crystalline rocks, 

 which occur in any and every age from the earliest times to the present. 



Especial stress has here been placed upon the characters and phenomena 

 of eruptive rocks, in hopes of bringing about a state of geology in which 

 the opposing eruptive and sedimentary agencies shall both have their proper 

 share, — which at present they do not have, on account of the extreme to 

 which the advocates of sedimentation have now carried their views. 



