960 GKABAU AND O'OONNELL THE GKAPTOLITE SHALES 



aljseiice of bottom organisms in these deposits is generally explained on 

 tlie basis of the great depth of the water. Wiman, on the contrary, recog- 

 nizing the difficulties attending T^apworth's explanation, regards the grap- 

 tolites as sedentary on ocean bottoms, where no other organisms can exist. 

 It lias l)een pointed out l)y both Lapworth and Ruedemann that the grap- 

 tolites may sink to the bottom nearer shore in quiet waters, for the pres- 

 ence of intercalated beds of sandstone and conglomerates in the graptolite- 

 bearing shales is clear proof of the proximity to the land ; but the former 

 author states, and the latter agrees with him, that the shales in the Moffat 

 region in Scotland were- clearly deposited far from shore in comparatively 

 deep water. 



The Problem Stated 



The problem before us, then, is this : Were the shales which carry only 

 graptolites, or in which other organic remains are rare, deposited in 

 waters too deep for other organisms to exist, or were these deposits, as a 

 rule, formed in deltas^ into the lagoons or bays of which only the plank- 

 tonic organisms would in general be washed from the sea at exceptionally 

 high tides or on the destruction of bars and similar barriers ? The present 

 preliminary note is to be regarded merely as a report of progress and it is 

 hoped that it will stimulate discussion of the subject. 



There are at least three lines of attack which might be followed in a 

 critical study of the lithogenesis of the graptolite-bearing shales. First, 

 there is the bionomic aspect, which is of great importance, particularly 

 since there are living representatives of the graptolites whose habitats 

 may be studied. A second line of attack is found in the consideration of 

 the lithologic character of the formations in which graptolites occur. The 

 third aspect to be considered is the stratigraphic, and this has turned out 

 to be of far greater significance than was expected and the only one which 

 we shall here take up. 



Typical Graptolite Shales 



There are two graptolite areas in Europe which above all others have 

 received the most careful attention of geologists and paleontologists : the 

 first is that of southern Sweden and the second is the Moffatdale section 

 in southern Scotland. The black shales in these two areas have been con- 

 sidered as the typical facies for these organisms, and have been cited by 

 authors as the ones which most clearly point to the deep-water origin of 

 the sediments. We shall therefore in the present discussion consider only 

 these two sections, especially since more detail probably is known about 



