Apeil 2, 1915] 



SCIENCE 



509 



areas by differential ciustal movement concomi- 

 tant with increase in volume of oceanic water 

 through deglaciation. 



5. The width of a submerged platform border- 

 ing a land area is indicative not of the amount of 

 submergence, but of the stage attained by plana- 

 tion processes. Other conditions being similar, the 

 longer the period of activity of such processes the 

 wider will be the platform. 



6. The principal value of the coral reef investi- 

 gation to geology consists not so much in what has 

 been found out about corals as in the study of a 

 complex of geologic phenomena, among which coral 

 reefs are only a conspicuous incident. 



Causes Producing Scratched, Impressed, Fractured 

 and Secemented Pebiles m Ancient Conglomer- 

 ates: John M. Clarke. 



The Devonian conglomerate lying beneath the 

 fish-beds of Migonasha, P. Q., is a characteristic 

 "Nagelflnh" filled with scratched, fractured and 

 deeply impressed pebbles. Specimens exhibited 

 indicate that the explanation of the phenomena of 

 impression by solution, as suggested by Sorby, 

 Heim, Kayser and others, is inadequate and that 

 the effects described are in large part actually due 

 to forcible contact resulting from internal friction. 

 Some of the pebbles show unqualified evidence of 

 glacial scratching and the entire mass is regarded 

 as an outwash from glacial moraine. 



Revision of Pre-Cambrian Classification in On- 

 tario : WiLLET G-. Miller and Cyril W. Knight. 

 During the past decade the authors have been 

 engaged in detailed work on pre-Cambrian areas in 

 various parts of the Province of Ontario. The re- 

 sults of this work, and that of other investigators, 

 have made apparent the necessity for revising the 

 age classification of the pre-Cambrian rocks, par- 

 ticularly in the use of the terms Huronian, Lau- 

 rentian and others. The following classification 

 and nomenclature have therefore been adopted by 

 the Ontario Bureau of Mines. 



Keweenawan. 



Unconformity. 

 Animikean. 



Under this heading the authors place not only 

 the rocks that have heretofore been called 

 Animikie, but the so-called Huronian rocks 

 of the "classic" Lake Huron area, and the 

 Cobalt and Eamsay Lake series. Minor un- 

 conformities occur within the Animikean. 

 Great Unconformity. 

 (Algkjman Granite and Gneiss.) 



Laurentian of some authors, and the Lorrain 

 granite of Cobalt, and the Killarney granite 

 of Lake Huron, etc. 

 Igneous Contact. 



Timiskamian. 



In this group the authors place sedimentary 

 rocks of various localities that heretofore 

 have been called Huronian, and the Sudbury 

 series of Coleman. 

 Great Unconformity. 



There is no evidence that this unconformity is 

 of lesser magnitude than that beneath the 

 Animikean. 

 (Laurentian Granite and Gneiss.) 



Igneous Contact. 

 Loganian. 



Grenville (Sedimentary), Keewatin (Igneous). 

 The authors have found the Keewatin to occur 

 in considerable volume in 8. E. Ontario and 

 have determined the relations of the Gren- 

 ville to it. 



Investigations by the junior author during 1914 

 have shown that certain rocks of the "classic" 

 Huronian area of Lake Huron, the "Thessalon 

 greenstones," that heretofore have been placed 

 with the Keewatin, are of much later age, being in 

 intrusive contact with the Animikean, as defined 

 in the above table. 



North American Continent in Upper Devonio Time : 



Amadeus W. Grabau. 



The history of North America in the Upper 

 Devonic has been worked out in some detail, on 

 the basis of physical stratigraphy combined with 

 paleontology. 



At the opening of the Upper Devonic, marine 

 waters were much restricted ia North America, the 

 greater part of the United States being exposed to 

 active erosion of the previously deposited Hamilton 

 or earlier formations, as indicated by disconform- 

 ities. The Tully-Genesee sea was restricted to cen- 

 tral New York, but extended northward over Can- 

 ada. Appalachia, Atlantica (the Old Eed Conti- 

 nent) and Mississippia were the chief continents. 

 The evidence pointing to the gradual southward 

 transgression of the sea over the eroded lands is 

 clear. Three open marine water bodies existed 

 throughout Upper Devonic time, each with its 

 Urals, (2) the western or North Pacific, extending 

 from central New York across Ellsmere land to the 

 Urals, (2) the western or North Pacific extending 

 across part of Alaska, (3) the eastern or Atlantic. 

 The latter entered the interior by way of a narrow 

 strait between Appalachia and Atlantica, permit- 

 ting the periodic invasion of the Atlantic or Tropi- 

 doleptus fauna. There may have been a fourth 

 South Pacific water body extending into Nevada, 

 but this is less certain. Three principal river sys- 

 tems are recognized in the lowland of Mississippia. 

 These have furnished the black mud for the black 

 shales which were deposited in embayments of di- 



