AuoueT 11, 1922] 



SCIENCE 



175 



interest in the study of clastic rocks, new terms 

 are needed to describe new phenomena. For 

 instance, conglomerates may differ greatly — not 

 only as to compositions but also as to origin, and 

 the phenoclasts should not always be called 

 pebbles. The petrogenesis of the sedimentary 

 rocks is intimately related to paleogeography and 

 paleobiology. The paper is a suggestion that 

 more attention should be paid to the "life- 

 history ' ' of sedimentary rocks. 



The Pre-Cambrian of western Patricia: E. M. 

 BuEWASH. A summary and compardson of the 

 pre- Cambrian complexes of the Lac Seul region 

 and of the Manitoba boundary north of the Win- 

 nipeg Eiver. 



Wednesday Apteknoon Session, December 28 

 Some of the physico-chemical properties of 

 eolloidal solutions and their relation to geological 

 processes: E. F. Bukton. The study of colloidal 

 solutions has to deal with the properties of sus- 

 pension of small solid or liquid particles in such 

 a liquid as water. Their geological importance 

 rests on the conditions under which such suspen- 

 sions are precipitated from their solutions, as, 

 for example, in the formation of deltas and, also, 

 on the curious effect of small traces of certain 

 jelly-like substances on the properties of soils. 

 Surface tension, electrical charges and molecular 

 motions play a role in bringing about the sta- 

 bility of such suspensions and in regulating con- 

 ditions of precipitation. 



The present status of the luedina problem in 

 southeastern Pennsylvania: Hakry N. Eaton. 

 Th9 Pennsylvania Geological Survey has investi- 

 gated recently the extent of the ridge-making 

 sandstone of the North or Blue Mountain in 

 southern Pennsylvania, and the stratigraphie and 

 faunal successions of the superjacent Silurian 

 and Devonian strata on the north side of the 

 mountain. Tentative conclusions were reached as 

 follows: For over one hundred miles in extent 

 the ridge-making sandstone is overlain conforma- 

 bly by the Clinton and probably is of Medina 

 age, apparently correlating with the Shawangunk 

 grit of tlie Delaware Water Gap region and west- 

 ern New Jersey. The upper Silurian and lower 

 Devonian limestones of the New York State series 

 were not deposited over the area immediately 

 north of the mountain, the Cayuga shale lying 

 directly below the Hamilton sandstone as far east 

 as the Lehigh Gap; isolated exceptions being a 

 thin band of Helderberg-Oriskany chert west of 

 the Susquehanna River valley, and a thin Onon- 

 daga limestone bed in SchuylkiU County, east of 

 Swatara Gap. 



The session then adjourned for a visit to the 

 Royal Ontario Museum under the leadership of 

 Dr. A. P. Coleman and Dr. W. A. Parks. 



Thursday Morning Session, December 29 



The Mackemie River Basin: D. B. Dowling. 



The basin of the Mackenzie Edver is underlain 

 by Devonian limestones and shales thinly covered 

 by Cretaceous and Tertiary sediments. The shales 

 and dolomites underlying the upper Devonian 

 limestones are of Middle Devonian age and in 

 places are petroliferous. The area which may be 

 considered as forming a possible oil field consists 

 of a belt showing comparatively little disturbance 

 between the crushed and metamorphosed zone -^f 

 the Rocky Mountains and the overlap of the 

 Paleozoic on the Archean to the east. The field 

 is divided by a line of folds which may be con- 

 sidered a spur of the mountains which cross 

 diagonally in a north and south direction. The 

 eastern part exposed around Great Slave Lake is 

 comparatively undisturbed. The portion west of 

 the mountain spur shows signs of partaking in 

 the earth movements. A triangular area with 

 upturned edge next the mountains shows minor 

 crumplings or lines of anticlines in a general east 

 and west direction near the northern border. 

 These terminate to the east in a probable fault 

 line or line of breaks in which the downthrow is 

 on the east side with the upthrow on the west 

 side showing only in the ridges which are anti- 

 clinal in section. The surface east of this line of 

 breaks is a flat plane, covered by Cretaceous, 

 Tertiary and later sediments leading to the hills 

 of the Franklin range to the east. The Devonian 

 shows erosion previous to the deposition of what 

 is probably Upper Cretaceous. Denudation of 

 the Cretaceous is indicated previous to the depo- 

 sition of the Tertiary and in this interval nearly 

 all the mountain building took place since the 

 Cretaceous is uplifted with the Devonian and the 

 Tertiary but slightly tilted. The structure of the 

 basin included within the pressure folds that 

 bound the part of the oil field west of the Frank- 

 lin range must be interpreted mainly from the 

 Cretaceous measures assuming that the uncon- 

 formity with the Devonian was a planation of 

 horizontal beds near sea level. The Tertiary 

 basins represent down warpings of the plane 

 underlain by Crestaceous which was to base level 

 of erosion at the inception of the mountain 

 building. Southward Cretaceous sediments are 

 present in great masses and form thick deposits 

 which were elevated by the earth stresses and 

 now form the plate-aus of the plains to the south. 

 The Cretaceous measures against which the pros- 



