GEOLOGICAL PAPERS. 105 



The shell beds near the top of the Dakota, in Ellsworth county, 

 containing Modiola pooli, contain a small univalve that has not been 

 determined. 



With so much for the Mentor, T will add a note or two on the 

 Dakota. 



Professor Mudge, in writing of the Dakota, in the First Biennial 

 Report of the State Board of Agriculture, said ( after speaking of the 

 irregular distribution of fossil-leaf beds): "The numerous indica- 

 tions show that the trees must have grown on islands near the shore- 

 line, and that the leaves were embedded in the marine sediment 

 immediately after dropping. Worm borings are also found in the 

 same strata with the leaves." 



Now, although this observation is probably in the main correct, I 

 have been astonished again and again to find how widely distributed 

 fossil vegetation is throughout the sandstones of the Dakota in this 

 region. Several times I have been shown very good specimens of fossil 

 leaves quarried or revealed in breaking rocks in localities that I had 

 looked over and passed as utterly destitute of fossils; and I have 

 learned by experience that diligent search will find traces of fossil 

 vegetation almost anywhere in the Dakota, which seems to me to 

 indicate that the ancient forests of the Dakota probably covered much 

 more of the surface than I had at first supposed, but that conditions 

 were much more favorable for preserving fossils in some localities 

 than in others. 



Reports have come to me several times, from sources that I can 

 scarcely doubt, of the finding of fine leaf impressions in the clay beds 

 of the Dakota revealed in cellar- or well-digging, and I regret that as 

 yet I have been unable to see any specimens of these. 



