Treeless Areas of the Northwest — Lelherg. 145 



in the immature stage, and that the new wing was produced from 

 internal growth, and ready to take the place of the injured one on 

 the emerging of the insect from the pupa, thus analogous with 

 the reproduction of lost limbs of spiders and crustaceans. 



If this be the case, which appears most likely, we may draw 

 the following conclusion: All the arthropods^ including true 

 insects, are capable of reproducing lost or much mutilated limbs, if 

 the same takes place previous to a moult or while yet in the imma- 

 ture stage. From the difference in habit of true insects from the 

 lower arthropods, we might also infer that the reproduction of a 

 lost limb would more readily and often take place among the lat- 

 ter. w4iile not absent in the former, as facts also show. 



March 2, 188(3. 



[Paper U.} 



SOME :N^0TES UPON" THE MORE RBCEi^-T FOSSIL FLORA OF N^ORTH DA- 

 KOTA AND AN INQUIRY INTO THE CAUSES THAT HAVE LED TO 

 THE DEVELOPMENT OF THE TREELESS AREAS OF THE NORTH- 

 WEST.- John B. Leiberq. 



A most noticeable feature of the prairies of North Dakota, 

 west of the Missouri river, is the immense amount of silicified 

 wood scattered everyw^here over the surface. 



This, in a region now almost devoid of arboreal vegetation, 

 naturally leads one to speculate on the causes that have operated 

 to destroy this ancient forest growth and prevent any other from 

 taking its place in modern times. 



We find that the land is covered by a rich and fruitful soil, 

 producing various kinds of herbaceous plants in great abundance, 

 and the average rainfall is sufficiently large to warrant us in not 

 classing the climate as arid. 



Various theories have been advanced to account for this ab- 

 sence of forest covered areas in the Northwest; one of the most 

 commonly accepted being that which ascribes the cause to the 

 annually occurring prairie fires, consuming with the dry grass 

 such seedlings as during the summer had found a lodgment. 



For some portions of the western prairie region this theory is 

 doubtless, in the main, the true one; but in the extreme North- 

 west, from the Rocky Mountains eastward, other causes luive been 



