310 UNITED STATES GEOLOGICAL SUBVEY—TERTIAET FLORA. 



positively to Miocene plants of Europe. I therefore admitted the forma- 

 tion as Miocene, while those of Marshall's were representatives of an older 

 Tertiary formation by their marked affinity to fossil plants which I had 

 examined and described from the so-called Great Lignitic of Mississippi, a 

 formation which I considered then as lowest Tertiary or Eocene. From 

 that time, and each year. Dr. Hayden sent me, as collected either by himself 

 or by members of his Survey, new lots of specimens, which were imme- 

 diately studied, and briefly described in his Annual Reports from 1870 to 

 1874. At first, most of the specimens were incomplete; therefore the deter- 

 mination of the species was sometimes doubtful. Later, in 1872, following 

 the instructions of Dr. Hayden, who wished me to study especially the 

 flora of the Lignitic, its distribution, and its evidence in regard to the age of 

 the measures, I visited the more important localities of the Western Terri- 

 tories where species of vegetable remains were obtainable: the Eaton 

 Mountains, Canon City, the Colorado Basin, and, in Wyoming, Carbon, Black 

 Buttes, Evanston, etc. I could there not only select more valuable materials, 

 but study in place some of the species from the comparison of numerous 

 fragments elucidating their characters. I had tb.en the assistance of my son, 

 Mr. L. Lesquereux, who greatly contributed (o the abundance of our collec- 

 tions. In 1873, 1 revisited, by myself alone, the Colorado Basin, and the more 

 important localities of the Bitter Creek series, adding considerably to the 

 collections of fossil plants of the Geological Survey, and procuring at the 

 same time the assistance of some gentlemen, who, becoming interested in 

 vegetable paleontology, have since then iurnished tome very fine materials, 

 described in this volume. The first of all, Rev. Arthur Lakes, has continued 

 his researches until now; his last communication, a lot of plants from the 

 Lignitic and another from the Cretaceous of the Hogbacks of Colorado, 

 came, to my regret, too late; and, though a few of the species which they 

 represent could be described in this volume, it has not been possible to have 

 them figured here. Then Col E. L Berthoud, also of Golden, sent, at differ- 

 ent times, some good specimens of very rare plants, especially those of a 

 Selaginella, which bears his name, and is the first species of this genus 

 hitherto known from Tertiary formations. 



When I visited Golden for the first time, I met there Mr. Wm. Cleburn, 

 who had already collected specimens of fossil plants from divers localities 

 along the Union Pacitic Railroad. As soon as apprised of the purpose of 



