294 GEOLOGICAL SURVEY OF THE TEEEITOEIEg. 



There may be some exceptional cases where both kind of evidence may 

 be in opposition, however, and afford reasons for dispute of authority. 

 For example, no Cretaceous invertebrate marine remains have been found 

 in the strata of the Lignitic above Point of Bocks, nor in the Bitter 

 Creek series above this point, nor in the whole extent of the Colorado 

 Basin ; hence the plants, being characteristic and Tertiary^ the whole 

 formation should be admitted as Tertiary, of course. But Vancouver 

 shows, as far as its flora is known, identity of characters of its fossil 

 plants with those of the Lower Lignitic, as known, from the above-named 

 stations; its relation is therefore defined as land formation, and this 

 should be to my persuasion considered as evidence of synchronism and 

 therefore of its Tertiary age, though the beds bearing Tertiary plants 

 may be locally and casually overlaid by marine strata with Cretaceous 

 animal-remains. This case has some analogy with that of the presence 

 of the bones of a Cretaceous Saurian at Black Butte. 



Conformability or uncomform ability of stratification proves very little 

 in regard to the changes which are considered as indicating a new epoch 

 or period. Of course the disturbances of wide-expanded surfaces of the 

 earth modify in various degrees the atmospheric circumstances, and, in 

 a less degree, however, those which govern the distribution of animals 

 under water. Therefore the changes in the characters of the floras or 

 the faunas may be more or less evident in correlation with these dis- 

 turbances. But these are more generally so gradual that they cannot 

 be remarked by traces of unconformability, and the consequences in 

 modifications of marine or land beings can be appreciated only at very 

 long distances of time. Gradual changes of this kind seem to have pro- 

 gressed during the whole period of the Cretaceous formations of the West, 

 from the base of the Dakota group to that of the Tertiary Lignitic, and 

 later still ; for in the whole vertical space occupied by the deposits no 

 unconformability of strata is remarked. But the concurrence of gradual 

 atmospheric modifications with those of the earth surface is distinctly 

 recognizable in the general character of the flora of the lower Lignitic 

 compared to that of the Dakota group, this being of a temperate 

 climate, while that of the Lignitic proves a subtropical one. Of course 

 the life under deep seas cannot be modified in the same degree and in the 

 same period of time. It is but very slowly influenced by land atmospheric 

 changes, and from this there is in some instances between the in- 

 habitants of the laud and those of the sea, a forcible geological discord- 

 ance, like that exposed at Black Butte by the Saurian and the plant's 

 remains wherein it was imbedded. 



Perhaps the more weighty objection against the deductions taken 

 from the characters of the Lower Lignitic flora is that of the unreliability 

 of comparison between the vegetable types of both continents in their 

 relation to supposed synchronous epochs. From this objection it is 

 said that we should not attempt, in regard to the distribution of the 

 North American fossil plant, to consider anything known of the geo- 

 logical relation of those of Europe. This objection appears at first 

 trifling, and it seems that it could be answered by the mere assertion that 

 as American paleontologists have constantly taken their points of com- 

 parison from Europe, in considering the relation of the animal remains 

 to the age of the strata where they were discovered, vegetable paleon- 

 tology should be allowed to use the same privilege ; for no section of 

 natural science can be defined and progress a priori or without means 

 of comparison, and where to find any if the European scientific do- 

 main should be closed. But iu this objection there is something more 

 than the mere privilege of comparison. It seems positive that from its 



