32 PROCEEDINGS OF THE PRIXCETOX MEETING 



Huronian, and went on to say that the Lower Huronian tillite of Ontario 

 occurred at various i)oints over an area of 20.000 square miles, and that the 

 materials from it had been accepted as glacial by most of the best glacial 

 geologists of the world. 



Dr. Whitman Cross : I have had opportunity to examine, in company with 

 Professor Atwood, the locality near Ridgway where the till beds occur below 

 the Telluride conglomerate and the San Juan tuff. This stratigraphic posi- 

 tion seems beyond question. The Eocene age of the tills is indicated bj' what 

 is known of the Tertiary history of the San Juan region, as set forth in the 

 Ouray and other folios of the Geological Survey. The volcanic eruptions of 

 the San Juan region began at or near the close of the Cretaceous, as shown by 

 the Animas beds near Durango of andesitic debris and containing dinosaur 

 and plant remains correlating them with the Denver beds. A flora has been 

 found in certain tuff beds of the Potosi volcanic series, in the central San 

 Juan, which has strong affinities with the flora of Florissant, Colorado, ac- 

 cording to Doctor Knowlton. This indicates an Oligocene or Miocene age for 

 those tuffs. The known record of long periods of volcanic eruption and ero- 

 sion between the deposition of the Miocene tuffs and the Telluride conglom- 

 erate make it almost certain that the latter is of Eocene age. The till fi^und 

 by Professor Atwood is presumably not much older than the conglomerate. 



Further remarks were made by Messrs. A. H. Purdue and Charles 

 Schuchert. 



ORIGIN OF PILLOW LAVAS 

 BY J. VOLNEY LEWIS 



(Al)stract) 



The peculiar stiiicture known as pillow lava (otherwise described as globu- 

 lar, spheroidal, ovoid, ellipsoidal, lenticular, and concretionary) has been ob- 

 served, chiefly in the last 20 years, at several localities in America. Numerous 

 examples are also known in the British Isles and on the continent of Europe. 

 The origin of the structure has been attributed to a great variety of causes, 

 including spheroidal weathering, spheroidal jointing, columnar jointing, with 

 subsequent movement of the columns on each other, concretionary action, ex- 

 plosive eiTiption (bombs in agglomerate), normal flow of lava on land, viscous 

 flow and fracturing of stiff lava, flow of lava under water, and intrusion into 

 unconsolidated sediments. i 



At all of the various localities that have been described the structure is 

 essentially the same as at several places in the later Newark basalt flows of 

 north central New Jei*sey, only one of which has been briefly described under 

 the name of pahoehoe. On the basis of its relation to the associated sediments 

 and of minor differences in the development of the structure itself, its origin 

 is here interpreted as a normal flow phenomenon, either subaerial or sub- 

 aqueous, when a highly fluid lava is rapidly chilled at the surface. In New 

 Jersey it seems to be wholly subaerial. 



Presented in abstract without notes. 



