1904.] HATCHP:R MARINE AND XON-MARIXE FORMATIONS. 361 



The points which it is especially desired to emphasize in the pre- 

 ceding pages are the following: 



1. That siratigraphic positio7i is not the only factor to be considered 

 in deter mini)ig the relative age of geologic formations. 



2. That an overlying deposit may have been contemporaneous in 

 origin 7oith that immediately underlying it instead of jnore recent. 



3. That in determining the relative age and working out the phylo- 

 geny of fossil forms the geographical position at which they occur in a 

 given formation is frequently of greater importance than the strati- 

 graphic. 



4. That the determiiiation of the approximate time within a given 

 period at which any stratum was deposited is often a more complicated 

 problem than has been ge?terally supposed and ca?mot always be esti' 

 mated by its positio?i relative to the base or sunwiit of the series. 



5. That every correlation should be based when possible on strati- 

 graphy, aided by the contained fossils and an ijiterpretation of those 

 physical conditions attending the deposition of the beds in question. 



6. That further studies are necessary relating to the physical con- 

 ditions that prevailed and the changes that were taking place over the 

 region occupied by tlie for77iatio7is discussed above during the period of 

 their deposition before we may hope to attain even a fairly satisfactory 

 correlatio7i. 



Note. 



Justice to the memory of my much lamented friend, J. B. 

 Hatcher, impels me to state my belief that had he lived he would 

 not have published the above paper without considerable revision 

 and alteration. The ideas that he has here attempted to express 

 were largely suggested or confirmed by the field study of the Judith 

 River beds in cooperation with the present writer during the 

 summer of 1903. A preliminary statement of our results has already 

 been published^ and a fuller account, which will shortly appear as a 

 bulletin of the U. S. Geological Survey under the title " Geology 

 and Paleontology of the Judith River Beds," was written by Mr. 

 Hatcher and myself last spring. On account of this association and 

 of my familiarity with the region and formations under discussion, 

 Hatcher came to me with his manuscript immediately after reading 

 it in Philadelphia and invited criticism. At least one other friend 



1 Science, n. s., Vol. XVIII, pp. 211-212, Aug. 14, 1903. 



