ABSTRACTS AND DISCUSSIONS OF PAPERS 397 



CHARACTERISTICS OF THE LASSEN PEAK ERUPTIONS OF MAY SO-22, 1915 

 BY BULIFF S. HOLWAY AND J. S. DILLER 



{Abstract) 



Lassen Peak, an old volcanic cone, unexpectedly burst into eruption in May, 



1914. The most violent explosions came during the period from May 20 to 22, 



1915. On the 22d a column of steam and volcanic dust was projected to a 

 height of at least 30,000 feet above sea, as measured by a nephoscope at lied 

 Bluff. A localized explosion projected rock fragments over a narrow, fan- 

 shaped zone extending eastward 10 to 15 miles. Some time during the latter 

 part of this period of activity the bottom of the crater was pushed bodily 

 upward, forming a plateau-like top. The eruptions caused floods down Hat 

 and Lost creeks on the northern slope of the mountain. The initial flood came 

 down the slope of the main cone with avalanche-like velocity, preceded or 

 accompanied by a blast which leveled forest trees beyond the flood area. 



Presented in full* extemporaneously. 



Discussion 



Prof. J. S. DiLLER read a brief paper on the recent activity of Lassen Peak. 



Mr. R. S. HoLWAY remarked that he had observed the eruption of Mount 

 Lassen June 1, and that red-hot debris shot up. One red-hot boulder was 

 seen to roll down from the crest. 



Further I'emarks were made by Mr. J. 0. Jones, 



The Society then adjourned for lunch. 



The Society convened at 3.15 o'clock p. m., with Prof. C. F. Tolman. 

 Jr., in the chair and J. A. Taff acting as Secretary. 



GEOLOGY OF PORTIONS OF WESTERN WASHINGTON 

 BY CHARLES E- WEAVER 



{Abstract) 



The oldest formations existing in western Washington are of probable Car- 

 boniferous, Triassic, and Jurassic ages. They consist of quartzites, cry.stalline 

 limestones, schists, slates, and a complex assemblage of intrusive and ex- 

 trusive igneous rocks of pre-Toitiary age. Deposits of Lower Cretaceous are 

 unknown within the State. The Tipper or Chico Cretaceous occurs in the 

 northern portion of the I'ugct Sound Basin as an extension of that from the 

 northwestern side of Vancouver Island. 



Presented in full extemporaneously. Kemarks were made by ^Ir. John 

 P. Bulwada. 



