TITLES AND ABSTRACTS OF PAPERS 125 



A third point concerns ori^'innl structures. The lK)ttom of San Francisco 

 Bay, like other present surfaces of deposition, is unduhiting. The deposit 

 formed in any particular century has marked basins, monoclines, and anti- 

 clines that are not due to deformation after deposition. Through differen- 

 tial settling, other structural features are developed, and two strata 500^ 

 or 100 feet apart may not be at all parallel. 



TILL ARGILLITES (PKLLODlTEii), J'RE-C AM BRIAN, PERMIAN, AND 

 PLEISTOCENE 



BY ALFRED C. LANE 



{Abstract) 



Glacial deposits are now generally accepted from the late Precambrian^ 

 Permian, and Pleistocene, and the till is generally recognized by having frag- 

 ments unassorted in size, shape, and composition (sometimes striated). Cor- 

 relative to the till, as Sayles has shown, are glacial brick-clays or till-argil- 

 lites largely composed of rock-flour particles, rhythmically banded and not 

 unassorted in size, but relatively so in shape and composition, the chemical 

 composition tending to approach that of the average rock and to be relatively 

 unleached. Illustrative analyses of rocks near Boston were given. 



Tresented witliout manuscript. 



Adjournment for luncheon was taken at 12.30 o'clock. 



After the noon recess the Society divided into three sections, to facili- 

 tate the presentation of the papers on the program. 



The main body was called to order at 2.20 o'clock p. m., President. 

 Merriam in the chair, and the program was resumed. 



TITLES AND ABSTRACTS OF PAPERS PRESENTED BEFORE THE AFTERNOON 



SESSION OF TUESDAY 



MISSISSIPPIAN TUFF IN THE OUACHITA MOUNTAIN REGION 

 BY H. D. MISER 



iAI)st7'act) 



Tuff of Carboniferous age occurs near the base of the Stanley shale, in the 

 Ouachita Mountain region in Polk County, Arkansas, and McCurtain County, 

 r»klahoma. There are three, and possibly four or five, beds of it, ranging in 

 thickness from 6 to 85 feet. All of them are very similar in lithologic char- 

 acter. The lowest bed is the thickest and most widely distributed ; it has been 

 mapped in detail in I)e Queen quadrangle, lying mostly in Arkansas, and to it 

 the name Hatton tuff lentil has been applied, for the reason that the best 

 known exposure is in a cut of the Kansas City Southern Railway one-half 

 mile south of the village of Hatton. The tuffs are compact, massive, and 

 tough; are generally liomogciieous. except for the presence of numerous chlo- 

 ritic "rjellets" that lie [.araJI*-! with the bedding, jiiid in color arc dai-k irray 



