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SCIENCE 



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



lact that these areas are coextensive with the 

 existing ocean currents. 



He gave some tables, based upon the West 

 American Pyramidellidse, showing that in this 

 group a remarkably small percentage of the spe- 

 cies extended over more than one area. He stated 

 that he considered ocean currents an important 

 factor in the distribution of marine organisms, 

 since they determined practically all the factors 

 entering into the environment in each area, viz., 

 temperature, food, salinity and transportation of 

 larval forms. 



Mr. Ulrich, replying to Mr. Willis's discussion, 

 said that most of Mr. Willis's objections had been 

 anticipated and accounted for in the paper read 

 at the previous meeting. It was denied that this 

 paper contained any statement indicating that its 

 author is inclined to the belief that marine cur- 

 rents in the Ordovician epicontinental seas of 

 North America were never capable of effecting the 

 deposition of sediments or of keeping the " bottom 

 clean of sediment in any portion of the submerged 

 seas." On the contrary, Mr. Ulrich mentioned a 

 number of instances of locally interrupted deposi- 

 tion attributable to current scour but claimed 

 that these were quite distinct in their causation 

 from the wider discontinuities which have been 

 similarly interpreted by Mr. Willis. It was fur- 

 ther denied that the paper sought in any wise to 

 discredit the effect of currents on the distribution 

 of marine organisms. Also that the deduction of 

 frequently shifting, limited and far from trans- 

 continental seas is founded solely on " an inter- 

 pretation of the distribution of faunas which dis- 

 regards all the limiting conditions of marine 

 environment except land barriers." Mr. Ulrich 

 insisted that before reaching his conclusions he 

 had considered more or less fully all phys- 

 ical as well as the purely faunal criteria that 

 seemed to have any direct bearing on the 

 problem. Considering that Mr. Willis has paid 

 perhaps as little attention to detailed field inves- 

 tigation of stratigraphic unconformities as to the 

 study of recent or fossil zoology, his short dis- 

 missal of conclusions based largely upon such 

 studies as " purely theoretical " seems rather un- 

 scientific. His remark respecting detailed paleo- 

 geographic mapping, when he said " that no one 

 is yet in a position to interpret the evidence for 

 limited intervals of time " is similarly unjust. 



Mr. Willis's statement that the Ordovician seas, 

 " if so land-locked as Mr. Ulrich supposed," would 

 nave become, like the Black Sea, " incapable of 

 supporting life that in any way approaches that 



of the Ordovician," was based upon a misconcep- 

 tion of Mr. Ulrich's meaning. As conceived by 

 Mr. Ulrich, Ordovician continental seas invaded 

 the land areas from one or another of the perma- 

 nent oceanic basins; with which they maintained 

 their connection and from which they derived 

 their faunas throughout their existence. 



Evidence of erosion is nearly always to be 

 found wherever a considerable hiatus in the 

 stratigraphic sequence is indicated by the fossils. 

 In view of the fact that such breaks in the 

 stratigraphic sequence commonly extend over by 

 far the greater part of the median area of the 

 continent, it is impossible to account for the wide 

 absence of the deposits and faunas by virtue of 

 any reasonably conceivable current efiBciency. Nor _ 

 can any other interpretation save emergence be 

 advanced to explain the established geographic 

 limitations of the Paleozoic faunas, especially 

 when no fauna of nearly similar age is found in 

 adjacent areas. 



The distribution of many types of littoral and 

 bottom-dwelling organisms takes place largely in 

 disregard of marine currents. There are other 

 types, however, notably the plankton and espe- 

 cially reef corals and sessile bryozoa, which propa- 

 gate by means of free-swimming larvse, that throw 

 much light on the direction and extent of the 

 currents in the Paleozoic continental seas. In 

 every case where the distribution of the latter has 

 been studied it is found that they rapidly become 

 fewer away from the point of invasion of the par- 

 ticular sea in which they lived. In most instances 

 they disappear entirely before reaching the inner 

 shores of the sea whose extent is determined by 

 continuity of deposits and the presence of other 

 organisms less dependent on currents for their 

 migration. This perfectly competent evidence, 

 therefore, is invariably opposed to Mr. Willis's 

 theory of great inland seas and of transconti- 

 nental currents which if present might have been 

 important factors in accounting for stratigraphic 

 hiatuses. 



Dr. R. S. Bassler called attention to the fact 

 that the trend of the discussion was losing sight 

 of the stratigraphic side of the question. These 

 distinct northern and southern faunas occurred in 

 distinct formations overlapping to extinction 

 either to the south or north as the case might be. 

 He added that these facts must be explained be- 

 fore currents can be held accountable for the 

 great faunal differences. 



Edson S. Bastin, 



Secretary 



