92 R. W. Chaney — A Fossil Flora. 



tion of aridity based on a lack of clastic sediments is open 

 to question, for it appears to be clearly established that 

 coarse clastic sediments will be deposited along the shore 

 of an arid tract by the runoff of the occasional rainfall. 

 Further, the moisture requirements of the land plants 

 show conclusively that the climate was not arid, for the 

 majority of the genera represented are found in moist 

 woods and thickets. The mixture of inland types with 

 marine deposits has been suggested to have been brought 

 about by stream transportation, though it is possible 

 they were transported seaward by the wind. The general 

 lack of clastic sediment in the diatomaceous shales may 

 rather be attributed to the low relief of the land mass 

 than to the lack of running water. For even though the 

 streams flowed seaward at so low a gradient that they 

 could transport little clastic sediment, the leaves of land 

 plants might readily be floated seaward by them. The 

 temperature conditions indicated by the flora are in accord 

 with those suggested by Jordan and Gilbert, as being 

 like those now existing in the region. 



The occurrence of terrestrial plant fossils in a marine 

 formation is unusual, as pointed out by White,^ and in 

 the case of specimens as perfectly preserved as those here 

 noted, indicates their deposition close to the shore. 

 Factors which may be supposed to have contributed to 

 this unusual preservation may be mentioned as 

 follows : — first, the lack of sediment in the water of the 

 streams which transported the leaves out to the sea, an 

 absence evidenced by the purity of the diatomaceous 

 deposits, would reduce the chances of the leaves being 

 macerated during their journey; second, the conditions 

 under which the diatoms were trapped and impounded in 

 bays'^ would favor rapid accumulation of the diatomaceous 

 shale, which in turn would favor the preservation of the 

 leaves ; and third, the fine texture of the diatomaceous 

 shale offers a matrix suitable for the formation of perfect 

 impressions of leaves enclosed in it. This combination of 

 circumstances, while unusual, should be the rule for 

 marine diatomaceous deposits and it may be hoped that 

 a careful search in such deposits in other localities will 

 result in the finding of other inclusions of terrestrial 

 plants in marine formations. 



* White, David, Value of Floral Evidence in Marine Strata as Indica- 

 tion of Nearness to Shores. Bull. Geol. Soe. Amer. 22, pp. 221-227. 

 ^ Jordan and Gilbert, op. cit. p. 14. 



