596 



CLARENCE N. FENNER 



A lack of homogeneity on a somewhat larger scale is indicated by 

 the fact that pieces of pumice from the same stratum of the ash- 

 fall show considerable variation from one to another in the amount 

 of basic phenocrysts they carry. These features are significant. 

 It seems as if turbulent motion in the lava when it was liquid 

 would have destroyed such inhomogeneities, especially the sharply 

 defined banding; hence, that solution occurred subsequent to the 



Fig. 17. — The stratified Katmai ash-fall, 8 to 10 miles south of the mountain. 

 Note the sharply defined character of the strata. The heterogeneous material on 

 top is the result of a small landslip since the deposition of the ash and pumice. Photo- 

 graph by B. B. Fulton, 1915. 



rise of the lava and while it was standing in a pool not violently 

 agitated. Evidently the magma did not become inflated at once 

 when pressure was removed in the depths of the earth, but rose 

 as a liquid and stood for a certain period in contact with foreign 

 material upon which it acted corrosively. 



A careful study has been made to determine the probable source 

 of this basic material. From samples of the ashy strata taken in 

 the field the pumiceous portion, which is greatly preponderant, 

 has been separated. The residue is found to consist principally of 



