BUFFALO SOCIETY OF NATURAL SCIENCES 51 



At a depth of about 400 feet below the surface, an abrupt change was 

 observed in the character of the strata, which were composed in great 

 part of sand, shingle, and boulders, the only fossils observed being the 

 vertebrae of a crocodile, shell of a Trionyx, and fragments of wood 

 very little altered, and similar to that buried in beds far above" 

 (154, 281). This boring was very evidently through the subaerial 

 portion of the delta, which was deposited at a time when the land 

 stood higher 'and when, probably, hilly areas now removed by ero- 

 sion or covered by deposits supplied coarser material near the seashore. 

 The variability in the types of deposits is shown and it is seen that 

 neither nodular limestones or conglomerates imply the presence of 

 the sea for their formation. The sediments of the present delta are 

 all fine-grained, the coarse deposits being found only at the foot of 

 the mountains. Moreover, the fine sediments are carried far out to 

 sea. "The sea, where the Ganges and Brahmapootra discharge their 

 main stream at the flood season, only recovers its transparency at 

 the distance of from 60 to 100 miles from the delta" (154, 279). In 

 speaking of the Mississippi river Lyell says: "The prodigious quantity 

 of wood annually drifted down by the Mississippi and its tributaries, 

 is a subject of geological interest .... as illustrating the 

 manner in which abundance of vegetable matter becomes, in the or- 

 dinary course of nature, imbedded in submarine and estuary deposits" 

 (154, 268). 



When the enormous transporting power of rivers is considered, 

 when we think of the amount and variety of sediments together with 

 terrestrial and fluviatile organic remains annually brought down to 

 the sea by rivers there to be mixed with the marine sediments and 

 the organisms riving in the sea, we find it not so difficult to realize 

 that the same phenomena happened in the past. The wonder would 

 be if such intermingling had not taken place, and one must indeed be 

 surprised to note how seldom it seems to have come to pass in the 

 Palaeozoic. Even admitting that land vegetation was mostly of a 

 primitive, easily destructible, non-vascular nature in the Palaeozoic, 

 we still must marvel that so few fluviatile and terrestrial forms were 

 carried out into marine deposits. 



If the above characteristics are kept in mind it will not be difficult 

 to formulate a certain number of criteria which may be used in rec- 

 ognizing a fossil delta or flood-plain deposit. That portion of the 

 delta adjacent to the mouth of the river will be characterized by an 

 alternation of marine and continental deposits, and these will be 



