HUXLEY ON HOMOTAXY. 489 



In America the same, conditions of sedimentation mark the place of the 

 particular fauna which we correlate with it. 



The Tully limestone is always impure, argillaceous, and not only varies 

 in thickness, but changes at its extremes into calcareous shales, and is fol- 

 lowed above by a fine, black bituminous shale. 



HOMOTAXY AND CONTEMPORANEITY. 



For all the region so far considered, the evidence is all in favor of the 

 view that in a general way and within comparatively narrow limits the 

 groupings of species into like faunas for the Middle and Upper Devonian 

 period were contemporaneous and not merely horaotaxial. 



In 1862 Professor Huxley, in the Annual Address of the President of the 

 Geological Society, advanced the view that the correlation of the geologic 

 formations of separate regions by likeness of fossil contents was correlation 

 of order of sequence (homotaxy) and did not imply contemporaneity. 

 He said : " For anything that geology or paleontology is able to show to 

 the contrary, a Devonian fauna or flora in the British Islands may have 

 been contemporaneous with Silurian life in North America or with a Car- 

 boniferous fauna and flora in Africa" (Q. J. G. S., Vol. XVIII, p. xlvi.). 



Although this is probably nearer the truth than the views then generally 

 held as to uniformity of geologic events for the world, the very methods of 

 research which Professor Huxley has done so much to promote enable us 

 now to predicate much more closely the actual temporal relationship of two 

 separate faunas. 



When we consider the area of northern Europe alone, including south 

 Devonshire, and extending eastward to Russia and the Urals and possibly 

 to China, the facts all point to a contemporaneity of the Caboides zone for 

 the whole region. 



Assuming this fauna to mark a definite point in the geologic series of 

 Europe, the place of its occurrence in the stratigraphic series may be called 

 the Cuboides horizon or zone, and the place the fauna occupies in the history 

 of marine faunas, of which it is one, the Caboides stage. 



We next raise the question, Is there any evidence of contemporaneity be- 

 tween it and the zone holding the homotaxial fauna in America? The Tully 

 limestone of New York, from both stratigraphic and paleontologic points of 

 view, is homotaxial with the Caboides Schichten of Kayser. 



The Tully Limestone and its Fauna. 



The Tully limestone is a zone of argillaceous limestone, ranging from a 

 few feet to over fifty feet in thickness, the outcrop of which crosses the 

 middle counties of New York state from Ontario to Chenango counties, but 



LXV— Bum.. Gbol. Soc. Am., Vol 1, 1889. 



