REPORT OP THE STATE PALEONTOLOGIST 1901 553 



process of calcareous sedimentation, it is more probable that 

 the calcareous mud was derived from the coast and was also 

 brought into that neighborhood by the motion of the water. 

 In taking account of all observed changes of deposition in the 

 Deep kill section, it is fairly safe to conclude that an alteration 

 in the direction of the movement of the water caused either the 

 calcareous or the silico-argillaceous mud to be deposited. 

 , The fine grained shaly partings between the beds were formed 

 during a period of quietness; but, while these partings of the 

 limestone beds are barren, those of the silico-argillaceous mud 

 beds are covered with graptolites; hence, at the period when 

 the currents brought the calcareous deposits and during the 

 intervening shorter calms, the higher levels of that part of the 

 sea were free from graptolites, while at the period when the 

 silico-argillaceous mud was brought in, the sea swarmed with 

 them. 



In an excellent exposition^ of the probable conditions of life 

 of the graptolites, Lapworth has concluded that the fine 

 grained black graptolitiferous sediment may have been de- 

 posited either in shallow or in deep water and that its forma- 

 tion depended not so much on depth as on the quietness of the 

 water. The conditions under which the Deep kill graptolite 

 beds appear to have been deposited seem in full accordance 

 with this inference, and from the character of the sediments 

 in that section as described above, it also appears that the 

 direction of the fiow of the water, which precluded the period of 

 quietness or which continued in the higher levels of the sea 

 must have been on the whole shoreward from the open sea, which 

 latter undoubtedly was the habitat of the graptolites. Thence 

 they came either as holo-planktonic free fioating organisms or 

 as pseudo-planktonic, fastened to seaweeds of the character of 

 the recent sargasso, as argued by Lapworth. 



The water from which the graptolites were settling was not 

 altogether free of current movement, as is shown by the parallel 



^Zeitschrift der Deutsch. geol. Gesellschaft. Jahrg. 1897. Heft 2, p. 

 239 ff. 



