338 



SCIENCE 



[Vol. LVI, No. 1447 



defining the range of animals whose range one 

 knows, in tei-ms of the ranges of plants and 

 animals whose range one does not know. 



Lutz' method of "Geographic Average" 

 (1921, Amer. Mus. Novitates, 5) involves con- 

 siderable calculation, which brings to light 

 with great effort the astounding information 

 that the "mid-range" of a northern species is 

 north of the "mid-range" of a southern species. 



He voices considerable discontent with the 

 zones as being indefinite and indistinct. Where- 

 upon he proceeds to define anew the undefin- 

 able and to redistinguish the indistinguishable. 



Inasmuch as all sharp changes in fauna are 

 dependent on similarly marked changes in 

 topography, it would seem reasonable to adopt 

 physiographic regions, instead of zones, 

 "major environments," and "geographic aver- 

 ages." 



Tor the United States this has been made 

 remarkably easy by the publication of "Physi- 

 ographic Divisions of the United States," by 

 Nevin S. Fenneman, Ann. Ass. Amer. Geog., 

 VI, 1917, which is the result of long continued 

 work on the part of a committee of the asso- 

 ciation. 



The lines of these divisions in many eases 

 agree with the zones and with the plant forma- 

 tions. This is to be expected for the ranges of 

 many animals should logically stop at a physi- 

 ographic break, or at a line of sudden change 

 in temperature or moistare, and the former 

 usually carries with it the two latter. 



Furthermore the use of these physiographic 

 regions clears the way for intelligent associa- 

 tion of animal and plant ranges with the 

 geology and soil conditions, and brings to light 

 routes of dispersal. 



For instance, this system makes clear the 

 presence of the Connecticut valley and the 

 Hudson-Champlain trough, in which many 

 southern forms extend north, but to draw these 

 on the map as Upper Austral, indicating 

 faunal identity with Piedmont Virginia (also 

 Upper Austral) is sheer falsehood. 



The beauty of this method, however, is its 

 ease of application. These regions can be 

 seen, their boundaries can be seen, and there is 

 seldom any doubt as to which region one is in 

 or from which specimens came. 



Of course, all animals do not respect physi- 

 ographic boundaries, any more than all animals 

 respect the lines drawn on maps to represent 

 faunal zones. 



None of our methods of indicating general 

 distribution is perfect. None ever can be. 

 Zoogeographers might well give some consid- 

 eration to the results of the "new geography," 

 and afford themselves some justification for 

 their title. 



Emmett Reid Dunn 



Smith College 



CLINKERTILL, A NEW METAMORPHIC 

 ROCK 



In view of the interest attached to the study 

 and identification of tillite a note about a rather 

 unusual form of till may be of interest. This 

 occurrence has never been described so far as 

 the writer is aware. 



Capping the northern bluffs bordering the 

 Missouri river in portions of sections 16, 17 

 and 18, Township 154 west, Eange 95 north, 

 Williams County, North Dakota, is a typical 

 bowlder-clay. This till lies on the truncated 

 edges of the gently easterly dipping, lignite 

 bearing. Fort Union Beds. In the sections 

 mentioned above a heavy bed of lignite, here 

 known as the Williston bed^ immediately under- 

 lies the drift. Here as elsewhere the Williston 

 bed has burned back from the outcrop baking 

 the overlying till in places to a thickness of 

 30 feet or 40 feet. The clinkertill so formed 

 varies in color from salmon-pink to dark brown, 

 brick-red being the common color. In selected 

 spots the material is fused to a porous, scoria- 

 like, mass but in most part is only slightly in- 

 durated by the heat. This baked till so formed 

 resists weathering and removal and forms the 

 capping of steep bluffs and buttes or mesas. 



The most common pebbles found in this 

 clinkertill are granite and limestone. The 

 granite pebbles appear to be unaltered by the 

 heat and the limestone pebbles but slightly as 

 they effervesce freely in hydrochloric acid. 



L. P. Dove 



NoKTH Dakota Geological Suevet 



1 Collier, A. J., ' ' The Nesson AnticUne, ' ' Bul- 

 letin 691 G., U. S. G. S., p. 213. 



