304 ANNALS NEW YORK ACADEMY OF SCIENCES 



land faun.T whose past history is preserved to us in the geologic record. 

 It involves only those minor changes of continental level (a few hundred 

 feet) of whose occurrence during the Pleistocene we have ample evidence. 

 On the other hand, if we assume such a Transatlantic land bridge 

 during the late Tertiary we must suppose an elevation of upwards of 

 five thousand feet, a huge disturbance of the isostatic balance of whose 

 possibility we have no real evidence; for the submerged channels so often 

 cited in support of these immense uplifts have been shown by Chamberlin 

 to be much more probably due to "continental creep," to the slipping 

 down, so to speak, of marginal sediments to a lower level. '-^ In any 

 case, there could be no evidence as to the period at which these old 

 channels were last above water. They may have been submerged since 

 the Permian, for aught we know to the contrary. Furthermore, we have 

 to explain the non-migration of a multitude of forms which got just so 

 far as conservative land elevations could carry them, but no farther. 



DISTRIBUTION OF PERCID^ 



Another instance upon which Dr. Scharff lays great stress is the dis- 

 tribution of the perches. Here, the false impression produced by the 

 use of a Mercator's projection map in plotting the distribution of north- 

 ern forms, seems to me to be very obvious. This map does not give the 

 northern regions in their true proportions or relations. Transferring 

 the distribution of this family as plotted by Tate Eegan, to a north polar 

 projection map we get the real relations and proportions with approxi- 

 mate correctness. It then becomes obvious that the perches are centered 

 around the drainage basin of the Arctic ocean. In North America they 

 have extended down the Atlantic coast drainage area and into that of the 

 Gulf of Mexico as far as the Eio Grande. In Asia they have been ad- 

 mitted by the old Hyrcanean Sea into the present Caspian and Aral 

 basins ; and a glance at the late Tertiary geography of Europe will show 

 how they have reached the drainage basin of the northern Mediterranean. 

 They are not now found in the Arctic drainage area of western North 

 America, Greenland or Iceland, where the environment, now or in the 

 Pleistocene, is amply sufficient to account for their extinction. What 

 need of a transatlantic land bridge to account for this distribution. 



123 There is another possihle explanation. The progressive hnilding out seaward of 

 barrier reefs around a number of separate centers until tboy .join<Hl into a platform 

 would naturally leave deep intervening channels, especially off the mouths of great rivers 

 where the influx of mud and fresh water hindered the growth of the coral organisms. 

 The submarine contours around the West Indian islands especially suggest this explana- 

 tion, which I offer tentatively for the consideration of my better-versed confreres. 



