FIELD NOTES ON MOUNT RAINIER, 1905 



is at least 1,000 feet above that on the right side. A 

 little way above the lower end of the glacier, on each 

 side of the canyon, a good opportunity presents itself 

 to study the contact of the lava and granite. The 

 granite at this place shows clearly that it was once a 

 land surface ; and one may note weathering for a 

 distance downward of seventy-five or one hundred 

 feet. The upper portion of the granite shows the usual 

 characteristics of weathering, namely, the conversion 

 of feldspar into kaolin, the oxidation of iron, etc. At 

 this point the lava overlying the granite is quite basic 

 and massive. The first flow reached a thickness here 

 of fully three hundred feet, and exhibits a fine develop- 

 ment of basaltic structure. 



In following up the canyon walls one observes that 

 the activity of the volcano for some time was char- 

 acterized almost exclusively by lava flows. In the 

 main the lava is an andesite, and is very generally of a 

 porphyritic structure. Some of the lava flows were of 

 great extent, and reached points many miles distant 

 from the center of the mountain. While the earlier 

 stages of the activity of the volcano were characterized 

 by lava flows of great thickness, by and by explosive 

 products began to appear, and interbedded with the 

 sheets of lava one finds bombs, lapilli, cinders, etc. 



It may be said in general that as the volcano grew in 

 years it changed more and more from eruptions of the 

 quiet type to those of the explosive character. It is 

 plain that a long period of time was consumed in the 

 making of that great volcanic pile, and that the erup- 

 tions were by no means continuous. It is clearly shown 

 that after certain outflows of lava, quietude reigned for 

 a time ; that at last the surface of the rock became cool 

 and that erosive agents broke it up into great masses of 

 loose stones. In later flows of lava these stones were 

 picked up and cemented into layers of pudding stone, 

 which are styled agglomerates. 



Rocks of an agglomerate type are well shown in the 



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