56 HYATT ON THE TERTIARY SPECIES 



layers, which are an inch or more in thickness ; second, the prolonged continuance of 

 conditions about equally fevorable to the rapid formation of limestone, or of clay strata ; 

 and third, the unfavorableness of the waters, at this time, to the existence of the 

 fish, which must have died in vast numbers. 



None of these f;icts, so far as the Pit Deposits are concerned, are in flxvor of the 

 vast periods of time which have been claimed by Darwinists, in order to account 

 for the changes which are supposed to have taken place in the fauna of the lake 

 during the Upper Period. 



There is only one foct which would seem to interfere with this conclusion. Some 

 of the " shell-sand beds " are mostly composed of broken shells, and it may be inferred 

 that they are wholly made up in this way. This may possibly be so, in some instances, in 

 the middle part of the deposits, but is of local occurrence, and not a general characteristic. 

 The limestones would come imder this head more than any other, as might have 

 been anticipated from their chemical constitution, but even here in most cases the matrix 

 is an even-textured argillaceous limestone, and " is not invariably composed of shell 

 fragments alone. 



It is very evident that the formation of the strata, either by precipitation or deposition, 

 was going on all the time, either as clay, limestone, or shell-sand, all over the area de- 

 scribed. The apparently regular interruption of the deposition of the clays and shell- 

 sands by beds of limestone are too local to indicate in any very positive way the constant 

 recurrence of periods of time or seasons when the waters of the lake were generally affec- 

 ted, and contained so little transported sediment of any kind, that limestone layers could 

 be formed on the bottom which would be continuous. These facts, the local distribution 

 of the beds of shell-sand in some clay strata, as in Section 3, and in several instances not 

 sketched in the section, in the East Pit and New Pit, the dark clay band d, Section 2, 

 in the midst of shell-sand, all appear to show that the unstratified beds were swept into the 

 spots where they are now found by currents of greater or less strength, and built up con- 

 tinuously during a period of time limited by the extra supply of water rushing down from 

 the drainage of the island, or the neighboring hills, or both. This extra supply of water 

 could only recur at certain seasons of the years ; therefore the unstratified beds either rep- 

 resent rainy seasons, and the intermittent local currents which they would naturally pro- 

 duce, or constant currents shifting in position from year to year, or season to season. 



If the latter theory is accepted it becomes exceedingly difficult to interpret the regularity 

 with which the coarser beds were locally interrupted by the limestone layers, without 

 assuming that there were years or periods of years, during which the currents flowed con- 

 stantly bringing in shell-sand, and then shorter or longer periods of months or years of 

 rest. These would occur at regular intervals during which the currents flowed somewhere 

 else to return again by some inexplicable fatality directly over the same spot, begin to 

 increase in volume, and move so first that shell-sand could be again transported. 



The latter hypothesis appears to me to present by far the greatest difficulties, besides 

 being contrary to experience. If we adopt the former, the Steinheim Pit Deposits show 

 a very limited thickness, for the most part of loosely aggregated materials which must 

 have been heaped up in a shorter time than one would be led to sujapose by the number 

 of new fossil forms produced and by a cursory examination of the strata. 



