THE HICKORY-NUTS OF NORTH AMERICA. 77 



and the fourth, the English walnut, is a native of Persia and the Cau- 

 casus. In times past the distribution was far different. What infor- 

 mation we have is derived only from a confessedly imperfect geological 

 record — a record exposed and explored as yet in the Rocky Mountain 

 region, in Alaska, Greenland, and Central Europe. In all of these 

 places species of either the one or the other genus have been found. 

 It is true that the determination of species or even genera is difficnlt 

 from fragments of leaves, but, as far as is now known, the following 

 are the facts : 



During that period of time known as the Cretaceous epoch, a tropic- 

 al climate prevailed over the whole of the northern hemisphere, even 

 to the pole itself, and probably also over the whole world. During 

 that time forests of trees flourished over the continent of North 

 America, over Europe, and probably Asia also. These forests were, in 

 many respects, similar in aspect to those which at present clothe por- 

 tions of the Ohio Valley. What species of trees lived in that part of 

 the country north of Virginia and Tennessee and east of the Missis- 

 sippi, it is now impossible to tell. But west of that river, and over 

 the larger part of the Rocky Mountain region, there grew forests in 

 which poplars, willows, oaks, beeches, sycamores, gums, magnolias, 

 and perhaps walnuts and hickories, were the prevailing types. The 

 remains of all but the last two have been found in the immense series 

 of Cretaceous rocks of the Western States and Territories, having for- 

 tunately been preserved in the deposits of the shallow seas or great 

 lakes which then occupied that part of the American Continent. The 

 genera mentioned are but a few of those of which remains have been 

 found, but they indicate a similarity in the flora then to that of the 

 present epoch. Many of the same genera are found in strata, of pre- 

 sumably the same age, in Alaska, Greenland, and parts of Europe, and 

 these facts indicate not only a similar climate in all these localities, 

 but a similar forest aspect. 



In the Tertiary formations, coming after the Cretaceous, the re- 

 semblance to modern trees is still more striking. During this later 

 period, that part of the Rocky Mountain region which had before been 

 under water was elevated above the surface, but immense basins re- 

 mained which were filled with brackish or fresh water. It is in these 

 fresh-water deposits that the abundant remains of ancient forests are 

 found. Many of the same types present in the Cretaceous period are 

 found in the Tertiary in still greater numbers. If there be any doubt 

 about the occurrence of walnuts and hickories in the former period, 

 there can be no question about their being in the latter one. The 

 number of species of oaks, poplars, figs, ashes, magnolias, and many 

 others equally well known, was increased. But we shall here consider 

 the two genera, the walnut and the hickory. 



In Europe one species of walnut is found in the Cretaceous rocks, 

 and a doubtful one is mentioned as found in rocks of the same age in 



