No. 373-] THE STUDY OF GRAPTOLITES. 13 
believe in the sessile mode of life of at least one species of 
Diplograptus by the finding of a slab (cf. of. cit., Pl. V) which 
showed a great number of well-preserved colonies spread out 
regularly in about equal distances from each other and arranged 
in a well-defined area. Giirich (96) and Lapworth (97) have 
advanced ideas lately as to the mode of life of the graptolites 
which correspond to each other, and which apparently explain 
many of the peculiar features in the distribution of these fossils. 
Lapworth found in Great Britain that graptolites may occur 
in all sediments, but that they are found only in great numbers 
in rocks containing a considerable amount of carbonaceous 
matter, and that the frequence of the graptolites is directly 
proportional to the amount of bitumen present and to the fine- 
ness of grain in the matrix. As the least motion in the water 
would carry away the light carbonaceous matter, Lapworth 
concludes further that the relative frequency of graptolites in 
a sediment depends also on the quietude of the water in which 
the rock was formed. This view is especially interesting to the 
writer in reference to his observation of a parallel arrangement 
of the rhabdosomes of graptolites in the Utica shale of the 
Mohawk Valley (97). This arrangement indicates the passing, 
during the Utica epoch, of a constant current in a northeast to 
southwest direction along the southern coast of the Adirondack 
crystalline area. As the alternation of graptolite-bearing shale 
and coral-line limestone in the lower part of the Utica shale 
proves, the current must have been strong enough to bring in 
the fine mud forming the shale, but cannot have been strong 
enough in the greater depths, where the deposition took place, 
to drag the well-preserved, delicate rhabdosomes for a long dis- 
tance. The occurrence of numerous perfect colonies in two 
localities is proof of the occasional. presence of almost perfect 
quietude. The latter, however, was the rare exception, the rule 
having been a slight motion, the traces of which can be found 
throughout the whole system of shales. The fine sinking mud 
undoubtedly assisted greatly in keeping the carbonaceous matter 
at the bottom. 
Lapworth further opposes the opinion, so often advanced, 
that the graptolites furnished the carbonaceous matter in the 
