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DURING forty years devoted to collecting and studying graptolites, the writer has observed that their distribution with respect to rock facies and association with other fossils is distinctive. To a far greater extent than any other fossil, the graptolites are bound to one definite rock facies, and they tend to produce pure faunas. They have not been discovered in great numbers mixed with benthonic or nektonic fossils in sandstones and limestones. These two facts—restriction to the black shales and tendency to segregate themselves from other species—have repeatedly impressed themselves upon the writer and have caused him to wonder as to the fundamental meaning.

The fact that most of the Paleozoic formations, regardless of their lithologic character, contain scattered individuals is dismissed with the interpretation that these are “stragglers.” They are greatly outnumbered by the non-planktonic forms. The significant fact is that domination of a fauna by graptolites amounts to exclusion of all except a few species, which also are characterized by an apparent aversion for any other rock facies, and which are so rare that active exploration and search of graptolite shales through the years has revealed only a comparatively small number. After surveying all the facts surrounding the occurrences of the graptolites and their associates, the writer is constrained to the opinion that these forms lived in sargasso-meadows of Paleozoic sargasso-seas in both the Atlantic and the Pacific oceans.

Part I of this Memoir presents first the evidence for this conclusion. It is shown that benthos ruled . . .

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