82 MONOGRAPH OF DURA DEN. 



But the position in the rock of the Dura Den fossils leads 

 clearly to the conclusion that they were suddenly and simul- 

 taneously imbedded in the sands and the silts of the period. 

 Their numbers, entireness, and general state of preservation, 

 evidently show that they have been overtaken by one and the 

 same cause of destruction, and instantly dropped to the bottom 

 of the waters. There is never a broken fin, nor a scale dis- 

 placed upon any of the specimens. They have not been 

 carried from a distance, nor rolled about for any length of 

 time. Everything indicates an immediate enclosure in their 

 soft sandy sepulchres, and, consequently, a rapid process of 

 silting up in the depths to which they sank. But for hundreds 

 of feet in the vertical thickness, up and down through the 

 rock, not a fragment or scale of a fish is detected. The mass 

 is completely non-fossiliferous, although consisting of several 

 varieties of materials, such as clays, marls, fine arenaceous 

 bands, and gritty beds. 



No long period, therefore, we may justly infer, could have 

 elapsed during the progress of accumulation, as within a given 

 amount of time many creatures must necessarily have perished, 

 and their remains been enclosed in the rocky mass. The 

 absence of fossils in a hundred feet of sandstone would warrant 

 the conclusion, from their natural term of existence, that 

 nothing like hundreds of years were spent in the accumulation 

 of the materials of the rock. And as with one series of the 

 formation, the same conditions, as we actually find them in 

 the lower series through immense depths of non-fossiliferous 

 strata, justifies the inference as to the proportion of the 

 element of time involved in the problem of their lithological 

 antiquity. 



There is another test of considerable value, furnished by the 

 fossil trees in the sandstones of the Carboniferous formation 

 around this district, by which to ascertain the rate of accumu- 

 lation in the materials of these rocks. The action of currents 

 in every case must be admitted as necessary for conveying the 



