THE LITTLE MISSOURI BAD LANDS. 639 



Of these leaf -prints the finest specimens collected in the Bad Lands 

 come from strata which have heen haked hy the burning coal. This 

 burned material furnishes a matrix of sufficient hardness to preserve 

 perfectly the mold and to endure the stroke of the hammer which 

 brings to light the hidden image, and so the life-history of Dakota, 

 like the history of some of the old Oriental monarchies, is revealed by 

 the cleaving of burned bricks. 



So far as I am informed, no systematic search for these fossil leaves 

 has ever been made. They occur on the surface in isolated spots, and 

 different localities furnish different as well as similar forms. The 

 baking to which the fossil-bearing beds have been subjected has, in a 

 measure, obliterated the distinction of strata, so that it is difficult in 

 any case to determine the exact horizon, or to say whether all the 

 leaves are from about the same level, and hence contemporaneous ; it 

 suffices our purpose to know that they are nearly so. At all events, in 

 strata such as these, and as geology reckons time, no intervals have 

 been very great, and we may omit discussion of the relative age of the 

 leaves, and consider immediately their kinds and meaning. We have 

 represented, in Figs. 3-12, leaves of the following genera : Platanus, 

 Po2ndus, Juglans, Corylus, Carpinus, Persea, Mens, Sequoia, Comics* 

 These names are all familiar, although we are not accustomed to see 

 them grouped together. Platanus is represented throughout the north- 

 ern Mississippi Valley by the sycamore, frequenting the water-courses 

 and rocky banks, and often attaining grand dimensions. Two species 

 of the genus occur in California, two in Mexico, and one in the far 

 Levant. Populus we know from our aspens, balm of Gilead, and more 

 than all by the cottonwood a prairie-tree abundant along our West- 

 ern rivers, and following the Missouri and its tributaries to the very 

 foot-hills of the Rocky Mountains. These trees all secrete about their 

 buds more or less of fragrant wax, and possibly from the tiny pits seen 

 at the base of the leaf of P. glandulifera exuded some such balsamic 

 gum which spread and polished the upper surface of the young leaves. 

 Of Corylus and Carpinus little need be said. The hazels and horn- 

 beams are sufficiently well known as characteristic of north temperate 

 forests everywhere. The genus Juglans we know from our invaluable 

 walnut, once common throughout the Eastern United States. A single 

 species is found also in Asia Minor and Europe. Cornus, the dogwood, 

 has some northern species. But the three remaining genera are more 

 interesting. Persea is a laurel, and laurels are especially tropical 

 plants, extending in hardier forms as evergreens into the sheltered or 

 milder parts of the temperate regions. This particular genus extends 

 along the Atlantic coast from Delaware southward, and is abundant in 

 the West Indies. Ficus is also a tropical genus, or, at least, occurs in 

 warm climates only, as in Florida, South America, around the Medi- 



* For the identification of these leaves, except one or two, I am indebted to Professor 

 Lesquereux. 



