INORGANIC CRITERIA 660 



It is obvious that the first suggestion of Iiabits and environment must 

 come from the morphology of the animals themselves, but it is equally 

 obvious that any natural collection of vertebrate fossils must be due to 

 unnatural conditions or processes of accumulation. If we are dealing 

 with animals of terrestrial habit, the concentration of their remains in 

 bone beds or in such quantities within any restricted area that they may 

 be profitably exploited by the collector will be due to one of two condi- 

 tions in almost every case : either they have been gathered together by 

 currents of water after death, or they have been overcome 1)y some catas- 

 trophe in the spot Avliere the remains occur. In either case the interpre- 

 tation of the climatic environment is sufficiently difficult, but it is 

 certainly more difficult in the usual case, where the remains have been 

 concentrated by currents of water after death, for here the sediments are 

 not in their original position and their history must be read before the 

 animal's habitat can be made out. The observer must have in mind, first, 

 the physical and chemical changes due to erosion and transportation, and, 

 second, the changes which have taken place since the time of deposition. 

 These are problems for the geochemist and the geophysicist, but the pale- 

 ontologist must for the time assume these tasks or leave the problem 

 unsolved. 



Unaltered Sediments 



Consider first the possibilities of interpreting the sediments on the 

 assumption that they have not been altered since their deposition. It 

 must first be determined whether they are lacustrine, palustrine, fluvia- 

 tile, littoral, or what-not. The determination of the character of the re- 

 ceiving basins of any area carries in itself far-reaching implications in 

 regard to the climate. Next the observer turns to the physical condition 

 of the sediments. The sizes and conditions of the grains and pebbles will 

 tell of the volume and velocity of the transporting bodies of water which 

 have borne the material from the land or in whose course it has been laid 

 down. A little careful study will generally reveal whether the floods 

 have been regularly recurrent or whether they have been sporadic. Wind- 

 .blown sand is not uncommon in many subaqueous deposits and its nature 

 may be determined by microscopic examination. All these things reveal 

 the climate. 



ISTow the chemical and mineralogical character of the sediments. Even 

 in the most altered sediments some portion will generally remain suffi- 

 ciently unchanged to reveal the character of the dominant rocks of the 

 land from which they were derived. If the land was dominantly liard 

 rock, the history of the eroded and transported sediments will be very 



