SIGNIFICANCE OF WIDE DISTRIBUTION OF GRAPTOLITES 235 



in Europe, and we may add that we have found the same late appearance 

 in the Deep Kill beds of New York. It is hence apparent that these 

 graptolites actually traveled from one basin to another, and with different 

 rate perhaps through their position in different depths. The great ma- 

 jority of the world-wide species, however, appeared together. If these at 

 all traveled with the ocean currents they must have, after once entering 

 these currents, been diffused in a, geologically speaking, immeasurably, 

 short time or have appeared synchronously. In that case the identical 

 graptolite horizons are the surest means of intercontinental correlation. 



We will now briefly consider the principal cases of wide distribution of 

 graptolites. 



The zone of Dictyonema fiabelliforme, which in Europe characterizes 

 the boundary between the Cambric and Ordovicic, is known as yet from 

 the Atlantic basin only, and its occurrence in the base of the graptolite 

 zones of the Levis Channel would indicate early Atlantic connections. 

 This horizon in Europe was first made the top of the Cambric, and lately 

 the bottom of the Ordovicic, and it has been also assigned in America to 

 the top of the first or bottom of the second system by several authors.^ 



The Beekmantown zones, as represented by the Deep Kill shales of 

 New York, are essentially Atlantic in their composition, but with some 

 undoubted Pacific elements, indicative of some connection with the Pa- 

 cific at times. The occurrence of these Beekmantown graptolites in 

 Arkansas and Nevada would seem to suggest a transcontinental connec- 

 tion with the Pacific. The principal Atlantic graptolites are fully at 

 home in the Pacific. We find, for instance, one horizon in Victoria, Aus- 

 tralia, characterized by Didymograptus hifidus, D. extensus (?), Tetra- 

 graptus quadrihrachiatus, T. serra, T. fruticosus, Dichograptus, Phyllo- 

 graptus typus, and P. sp. And the fact that the differences in the time 

 of appearance of some important forms between Australia and Europe 

 (as the later appearance of Loganograptus logani and earlier appearance 

 of Didymograptus hifidus in Australia) are exactly duplicated in our 

 Deep Kill zones, and the presence of Gonigraptus thureaui in both Aus- 

 tralia and the Levis Channel are strong arguments not only in favor of 

 some connection of the Levis basin with the Pacific Ocean, but even of 



3 Doctor Ulrich writes me regarding the age of tliis horizon: "The Dictyonema ffabel- 

 liforme and the main Tetragraptus zones I regard as in large part if not entirely older 

 than the lower part of the 4,200 feet of Canadian (Beekmantown) limestones in central 

 Pennsylvania. This is indicated by the facts (1) that mutations of Didymograptus 

 hifidus, D. amplus, and Phyllograptus iltcifolius occur in northern Arkansas only in 

 lower Canadian deposits, and (2) that the conglomerates at Quebec contain late middle 

 or upper Ozarkian trilobites." 



XVII— Bull. Geol. Soc. Am., Vol. 22, 1910 



