438 MEMOIRS OF THE CARNEGIE MUSEUM 



dammed up by the ice, and transfonued into lakes (Lake Monongaliela of White, 

 1896, and Lake Ohio, cf. Jillson, 1893. p. 19, and Map, PI. 5, with the necessary 

 restrictions), and this led to the I'esult that the colonies uf crawfishes bel«)n;L;in,i;' to 

 the southern (upper) parts of these rivers became sharply sejiarated fi-Din each otiier, 

 and I think that the foidmcji toivard llie formation of three species {('. jtritjiiinpnis, C. 

 sanhonn, C obscurus) is (Jirecth/ (hie to ilris process amJ Id iiIii/-'<i<>(/roi)]uc(il comlifiovs 

 prevailinij in tlie earlier part of the (jlacial Period (Kaiisan or Prekansai}, cf. Hice, 

 1903, p. 300). 



Finally these lakes were connected and drained off toward the southwest, thus 

 forming the present Ohio River (Postkansan, but liefore the Wisconsin stage, cf. 

 Hice, 1903, p. 29rl); the areas of the three forms of crawfishes were reunited, but 

 the different parts of the new Ohio drainage are occupied by diffei'ent forms of the 

 projiiiKpius-gixmp, remaining in their original areas; the ui)per Ohio is character- 

 ized by ('. oJ>scnras. the middle Ohio by C propinqaus sanhoriii, and the lower Ohio 

 by ('. propineprus. 



]'>ut additional changes took place in Postglacial times. According to the pres- 

 ent distril)Ution these must have been greatest in the case of C. propimpeus. 

 Almo.st the entire range of this form lies within the ijlaciated area, and thus it is 

 beyond question that its present distribution is largely due to the Postglacial migra- 

 tion northward and northeastward.'' This migration possibly began at an earlier 

 date than in the case of the other two forms. We know that in southern Indiana 

 and southwestern Ohio an early i-etreat of the southern border of the ice took place, 

 as is indicated by the presence of lllinoisan drift soutli of the early Wisconsin border 

 (cf. Leverett, 1902, PL 2 and PI. 11). Tliere also was considerable recession of the 

 ice of the Maumee-Miami glacial lobe in the earlier and later Wisconsin stage, while 

 in central and eastern Ohio and western Pennsylvania (Scioto glacial lobe and 

 (irant River glacial lobe) only in the later Wisconsin stage did recession take place 

 [cf. Leverett, ibid., and PI. 13 and PI. 15). Toward the end of the later Wisconsin 

 stage large lakes began to form in front of the receding ice, and this happened first 

 in the western part of this region. Tiie first lake thus formed was Lake Maumee 

 (Leverett, p. 710 tf., PI. 20 and 21). which had an outlet toward the west and south- 

 west (Fort Wayne outlet; see also Grabau, 1901, p. 58). Lake Maumee was situ- 

 ated in northwestern Ohio, in the present Huron-Frie basin, and thus we see that 

 the latter was opened first in its western part tcj an immigration from the southwest 



^' A loss of territory must liave occurred in the sontli, C. propinqints losing ground in competition with C. rusticus 

 which was pushing on from the south. This matter does not belong to our present investigation, but attention should 

 be called to it. 



