512 NEW YORK .STATE MUSEUM 



(2) to the fineness of the sediment, and (3) to the length of the time of deposi- 

 tion. He concludes, further, that the graptolites did not produce the car- 

 bonaceous matter of the black shales by their decomposition, for they are 

 never found as partly decayed rhabdosomes, which pass into the surrounding 

 carbonaceous matter. That they did not live as sessile benthos attached to 

 the bottom of the sea can be inferred from the fact that the}?- never pass 

 vertically from one bed to the other, but are always spread out as if they had 

 slowly settled in tranquil water. 



The distribution of the typical black graptolite shales of Great Britain 

 shows further that they preserve their strikingly thin bedding and fine grained 

 character over enormous distances in a northeasterly and southwesterly strike, 

 but that, when traced in the direction from northwest to southeast, they 

 rapidly change into coarser sediments and graywackes, or into deposits of 

 shallow water with surface currents. This northeast-southwest extension is 

 now, for certain reasons, to be considered as running parallel to the protozoic 

 coast line, and the graptolite beds in England are hence dependent, in a sense, 

 on the old coast lines of that period. While the absence of clastic material in 

 the Moffat shales proves their deposition in deep water distant from the coast, 

 the black graptolite shales embedded in the contemporaneous coarser sedi- 

 ments of Girvan and Wales were deposited at a much faster rate. Hence the 

 same black, fine, muddy sediments can be formed m deeper and shallower 

 water, and not the depth but the tranquillity of the water is the most 

 essential factor. 



As the graptolites did not furnish the cellulose material for the car- 

 bonaceous shales, it is to be inferred that this was derived from plants. On 

 account of the scarcity of land plants in the lowest Ordovicic, there remains, by 

 exclusion, the derivation of the carbonaceous matter from drifting seaweeds. 

 The enormous masses of Sargassum which, torn from the coasts, continue to 

 live while drifting in the oceans as pseudoplankton, are cited as a recent 

 example for comparison. 



The bands of carbonaceous beds Avould then, according to Lapworth, 



