BUFFALO SOCIETY OF NATURAL SCIENCES 83 



inland, as they are today, and might come to rest in the very muds 

 in which the river organisms were buried. Likewise, in the low-lying 

 portions of the flood plain near the sea, occasional high tides or in- 

 undations, through the wearing away of sand-bars, might allow the 

 salt water to enter, carrying some marine shells into those regions. 

 Then the fossil fauna would show a large number of forms belonging 

 mainly to one phylum, the arthopads, and occasional single speci- 

 mens of members from other phyla. If the opposite conditions pre- 

 vailed, and the fragments of the arthropods or their exoskeletons 

 were blown to sea, then the fossil fauna would reveal many marine 

 organisms, complete and well preserved, from all or nearly all of the 

 invertebrate phyla, and occasional fragments of another group of 

 organisms which were not well preserved and whose occurrence in 

 such surroundings seemed anomalous. 



Brackjsh-Water and Estuarine Deposits and Faunas. It 

 has been shown that at the present time there is no such thing as a 

 brackish-water fauna made up of classes of organisms different from 

 those found in neighboring marine and fresh waters. It might be 

 extremely difficult to recognize from the sediments and fossils that 

 any fauna had lived in brackish water, because unless the salinity 

 had been reduced so much that it was nearly that of fresh water the 

 fauna would not appear to be very different from a typical marine one, 

 except that it would be dwarfed and would contain few species. An 

 estuarine fauna would likewise be difficult to recognize from the fos- 

 sils. These would, however, be likely to be fragmentary, even com- 

 minuted to microscopic size, and larger forms would be found only in 

 the sands and coarser deposits along shore and not in the estuarine 

 deposits proper. It has been seen that the conditions in an estuary 

 are not favorable for supporting life. The tidal scour, the churning 

 up of the water, keeping the sediments constantly in suspension, the 

 sudden change in salinity twice every day, are environmental factors 

 not at all conducive to attract marine animals which can find more 

 stable and beneficial conditions along the coast on both sides of the 

 estuary. Thus, we saw that in the Severn the organisms whose com- 

 minuted remains were found in the muds lived many miles away in 

 the quieter waters north and south of the estuary. In the geologic 

 column we shall probably rarely be able to recognize estuarine de- 

 posits from the faunas, but if at all it will be from the nature of the 

 sediments, their lithological characters and sources. 



