AREAL DISTRIBUTION OF THE LIGNITIC FORMATIONS. 7 



and further, that there occurs in the same formation a substance like petro- 

 leum in color and consistence, but without odor ; that from the specimens 

 brought home by the last-named traveler from the vicinity of Fort Union, 

 near the confluence of the Yellowstone and Missouri Rivers, we derive incon- 

 testable proofs of a fresh-water formation. Among other strata exposed in a 

 cliff near the fort are thin beds of clay and argillaceous rock, both containing 

 three or four species of fresh-water univalve shells. There is besides a rock 

 twenty or thirty feet thick, which also contains proofs of fresh-water origin 

 in bivalve shells, leaves of deciduous trees, and bones apparently of mam- 

 miferous animals. 



Details in accordance with those given above are reported from the belt 

 of the Lignitic surveyed north of the limit of the United States and British 

 America. They extend to Vancouver, even to the Arctic land of Disco, 

 Greenland, and southward along the Pacific slope to the southern extremity 

 of the continent. They are, however, still less precise, and evidently Mr. 

 Taylor refers to the Tertiary coal deposits of different geological ages. 

 Hence, we have as yet nothing definite in regard to those mentioned coal 

 strata. Even we may say that scarcely anything positive was known of the 

 great North American Lignitic when Dr. F. V. Hayden undertook the work 

 of exploration and began his researches, in 1854. It is therefore from the 

 numerous publications of reports and memoirs of the celebrated geologist 

 that I have to take most of the reliable facts exposed in this introduction. 



I cannot enter into the examination of Dr. Hayden's researches without 

 remarking on the accuracy of the data which he has exposed in his numer- 

 ous Reports and Memoirs on the Geology of the Western Territories. Begin- 

 ning in Kansas and Nebraska, he has followed the explorations foot by foot, 

 so to say, not omitting a single fact worth the attention of the geologist. 

 Collecting specimens of ore, of minerals, of animals, of plants, he has by and 

 by traced the outlines of the present and ancient history of these Western 

 Territories; and calling to his assistance all the specialists who might ren- 

 der his work more complete, he has filled the pages of a truly invaluable 

 record. For now, the natural history of those .western regions, mostly 

 unknown a few years ago, is exposed as distinctly and precisely as may be 

 that of any of tlie oldest States of the Union. The agricultural and mineral 

 resources, the geographical and stratigraphical distribution, the fauna and flora 

 of the present epoch, those of the former geological periods, even the phys- 



