GEOLOGICAL SUEVEY OF THE TEEEITOEIES. 95 



the basins in which they accumulated. By tracing the outline of these deposits, Dr. 

 Hayden has demonstrated that sheets of fresh water once covered surfaces in this por- 

 tion of the continent which, in extent, rivaled the great chain of fresh-water lakes 

 which exist elsewhere in our country at the present day. There is, therefore, every rea- 

 son to believe that the remains of ligueous plants which compose this collection were 

 derived from trees which grew along the shores of the lakes and streams of the tertiary 

 continent ; that then, as now, alternations of seasons prevailed, by which the foliage 

 of these trees was periodically detached, and that, falling into the waters beneath, or 

 near them, and sinking to the bottom, they were enveloped in mud precisely as leaves 

 of our sycamores, willows, oaks, &c, accumulate at the bottom of our streams and 

 lakes at present. 



In comparing the group of plants here presented to us with those now living upon 

 the surface of the earth, any one will be at once struck with the resemblance which 

 they present to the flora of the temperate zone, and more particularly with that of our 

 own country. In their study I have constantly found that on making comparisons 

 with the plants of remote, and especially tropical countries, an entire want of resem- 

 blance or affinity at once discovered itself, and the only instructive comparisons made 

 have been with the present vegetation of our country, that of the miocene tertiaries of 

 Europe, and with the living plants of China and Japan. There is every reason to be- 

 lieve that future observations will make immense additions to this flora, and satis- 

 factory comparisons and generalizations will only be possible when a far more com- 

 plete series of its plants can be subjected to study. It is also true that as yet little 

 other than the leaves of these plants have been collected and employed in the deduc- 

 tions made from them. From the character of the sediments which inclose these leaves, 

 it is quite certain that the fruit and seeds are also preserved in the strata from which 

 they were derived; but as they are less conspicuous and noticeable than the leaves, they 

 are little likely to be found unless especially sought, and it will only be when they are 

 made the special objects of search that they will be discovered, and lend their import- 

 ant assistance in the solution of the problems which the leaves present. For the 

 want of such information as these organs would supply, some of the material included 

 in the collection does not now admit of satisfactory classification, and the references of 

 some of the leaves to the genera under which they are placed must be regarded as pro- 

 visional and liable to modification by further research. Quite a number of these plants 

 are, however, so largely represented in the collection, so well preserved, and so clearly 

 allied to the genera and species with which we are familiar, that they constitute fair 

 material from which to infer the general characters and affinity of the flora of which 

 they form a part. In this list may be mentioned the Glyptostrobus, of which the stems, 

 bearing the leaves of different forms, the cones and the sterile capitula are all present, 

 and so closely resemble the specimens described by Professor Heer from the miocene of 

 Europe, that they might also be considered the originals from which his figures were 

 taken. The living analogue of this is G. heterophyllus of China. 



The Taxodium now described is evidently a close analogue of Taxodium duMum of the 

 miocene of Europe ; differing from that well-known species only in the uniform round- 

 ing of the bases and summits of the leaves. 



The fossil which has been doubtfully referred to Sequoia Langsdorfii would probably 

 be regarded by foreign botanists as identical with that species, but for the reason given 

 in the remarks upon that plant, it seems to me quite doubtful whether it was a Sequoia, 

 and more probable that it was a Taxodium allied to our deciduous cypress. 



The great fan palm (Sabal Campbelli) collected by Dr. Hayden seems to be a repre- 

 sentative of Sabal major of the European tertiaries, and Sabal palmetto of our Southern 

 States. Frym both these, however, it is distinguished by the large number of folds in 

 the leaves, and from S. major by its flat, unkeeled petiole. The plate now given of this 

 species represents the under surface of the leaf and petiole, but the collection also con- 

 tains fragments showing the upper surface ; and in the collections of the northwestern 

 boundary commission are specimens obtained from the coast near Frazer's Eiver, which 

 exhibit in fine preservation the upper surface of the base of the leaf and a large portion 

 of the petiole. From these latter specimens the species was originally described in the 

 journal of the Boston Natural History Society. 



The numerous species of Populus, of which figures are now given, will not fail to 

 attract the attention of those whose interest runs in this direction. Several of them 

 seem to be new to science, and show, for the most part, a greater affinity AYith the for- 

 eign poplars, P. alba, &c, than with the specimens more common on this continent, 

 though a single one, P. genatrix, evidently belongs to the group of which our balsam 

 poplar may be taken as a type. The little species described under the name P. rotun- 

 difolia presents some anomalies in form and structure as compared with most of our 

 poplars, but its resemblance to another species contained in this collection, P. clliptica, 

 and one contained in the collection of the Northwest Boundary Commission, which I 

 described under the name P.jlauellum, have induced me to class them together. Among 

 living species it has a striking analogue in Populus pruinosa now growing in Songaria. 



The several species of Platanus which the collection contains form a striking andSn- 



