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SCIENCE 



[N. S. Vol. XXXIII. No. 843 



locked as Mr. Ulricli supposed, the food supply 

 would fail and the condition which has been 

 reached by the present Black Sea whose waters 

 are incapable of supporting life that in any way 

 approaches that of the Ordovician, might be 

 reached. 



Referring to the paleogeographic maps which 

 have been issued by Dr. Schuchert and to Mr. 

 Ulrich's views on the details of paleogeography 

 in the Paleozoic age, Mr. Willis held that no one 

 is yet in a position to interpret the evidence for 

 limited intervals of time. The study requires the 

 most searching investigation of the different lines 

 of evidence and a better understanding of the 

 principles that shall govern the interpretation 

 before any more than general outlines of the 

 geography can be mapped. Dr. Schuchert's maps 

 represent the distribution of faunas, and for each 

 fauna which is mapped they represent the extent 

 of the temperature, food and other conditions that 

 determined its habitat. In this respect they are 

 of the highest value. Where, however, the ab- 

 sence of a fauna or a formation has been taken 

 as a proof of the existence of land without evi- 

 dence of erosion, the maps are misleading, since 

 the alternative hypothesis that the area was sub- 

 merged, but was inhospitable to that particular 

 fauna, has not received due consideration. The 

 causes which now maintain the great equatorial 

 currents flowing from east to west have been in 

 operation since the oceans were established. Cur- 

 rents and eddies diverted from these main currents 

 by the continental platforms have necessarily 

 been features of all continental seas, and no study 

 of the life conditions of extinct faunas can be 

 adequate that does not take account of the biolog- 

 ical and physical effects of such currents. Hence 

 any inference based upon faunas which are inter- 

 preted without reference to currents must be 

 fallacious. 



In regard to the subject of marine scour, espe- 

 cially by the Gulf Stream, Mr. Willis presented 

 a map showing the submarine deposits of the 

 Caribbean, Gulf and North Atlantic, as given by 

 Agassiz in the " Three Cruises of the Blake." 

 That map shows that sediment is deposited under 

 the axis of the Gulf Stream between Cuba and 

 Florida along much of the coast, for the depth 

 of the water is there greater than the depth of 

 the current, which does not reach much below 

 100 or 150 fathoms, but where the water is shal- 

 lower or where the current turns from its easterly 

 to a northerly course, it is carried against the 

 bottom and at those points there is a hard lime- 



stone bottom covered only by fragments of broken 

 rock and coral, and washed clean by the current. 

 It also appeared from Agassiz's discussion of the 

 action of the dredge that the areas which he 

 mapped as limestone plateaus have a hard and 

 uneven rock bottom, and although the Coast Sur- 

 vey charts over much of the areas so mapped by 

 him show soundings of sand and broken shell, the 

 evidence is that the material brought up on the 

 sounding line is but a superficial coating, locally 

 covering the vmeven limestone bottom. Admiral 

 Pillsbury has shown that the volume of water 

 passing a section of the Florida Straits in one 

 hour amounts to nearly 90 billion tons. It has a 

 velocity which varies from two to three and one 

 half knots. The energy of this mass of water 

 could not be lightly checked. Should the sea 

 bottom between Florida and Cuba be gently ele- 

 vated by an orogenic movement, or should the 

 general level of the ocean be lowered so that the 

 current would reach the bottom, the silt which is 

 now deposited beneath the current would inevi- 

 tably be swept away. A barrier to the current 

 would only be established in case the orogenic 

 movement raised the bottom more actively than 

 the current could erode it. This could scarcely 

 occur unless the bottom were hard rock. The 

 condition which is thus suggested is that which 

 may be considered as a working hypothesis in 

 explanation of the imbricated limestone of the 

 Ordovician in the eastern United States. It is 

 postulated that there was an extensive sea which 

 was open from south to north, and through which 

 marine currents circulated, as is indicated by the 

 distribution of life. The sea deepened or shal- 

 lowed from time to time, and there were basins 

 which, according to the great thickness of sedi- 

 ments laid down in them, deepened, while other 

 areas apparently remained as saddles between 

 them. If this interpretation of the physical and 

 faunal facts be correct, it is reasonable to suppose 

 that the currents were at times brought within 

 reach of the bottom and that a condition of non- 

 deposition supervened locally during a more or 

 less prolonged interval. 



The discussion was continued by Rear Admiral 

 J. E. Pillsbury, who had command of the Coast 

 Survey steamer Blake for five years and spent a 

 large portion of each year investigating the Gulf 

 Stream. He first explained the methods formerly 

 used of gauging marine currents by cans floating 

 on the surface and submerged below, and then 

 the methods adopted by the Blake of anchoring 

 the vessel in the stream and measuring the 



