BALTIC EEGION 589 



stones, both of which form transition beds to the Lower Beekmantown or 

 Little Falls dolomite. 22 



The great faunal difference between the West European early Ordovicic 

 and that of eastern North America is probably to be explained by the 

 difference in origin of the faunas, the Beekmantownian being primarily 

 a Boreal 23 or northern fauna in the east and northeast and a South Pa- 

 cific fauna in the south and west, while the "West European limestone 

 fauna is of North Pacific or of Siberian origin. The graptolite fauna, 

 however, was undoubtedly, in part at least, existent in the Atlantic. 



The close association of the Ceratopyge limestone and the limestone 

 with Megalaspis planilimbata in the Trollmen region above noted, and 

 the occurrence of the Lower Didymograptus shales above it, precludes the 

 possibility of the existence of a pronounced hiatus (if any) between the 

 Lower Eed Orthoceras limestone {Megalaspis limbata limestone) and the 

 Lower Didymograptus shale, because M. planilimbata and M. limbata 

 are found associated in the same beds in regions where the Lower Didymo- 

 graptus shale is wanting as in Dalarne, discussed further on. It would 

 thus appear that the Lower Didymograptus shale, when present, replaces 

 a part or all of the Planilimbata limestone and perhaps a part of the 

 Limbata limestone as well. Farther east, in Westergotland, at (Ede- 

 garden, the Lower Didymograptus shale is wholly replaced by the Mega- 

 laspis planilimbata limestone, which, as we were able to judge under the 

 expert guidance of Professor Wiman, is here intimately associated with 

 the Ceratopyge limestone, which in turn rests disconformably on the 

 Upper Cambric Stinkkalk with Peltura and Sphgeropthalmus. 



22 1 am well aware that Ulrich separates the Little Falls dolomite from the Beekman- 

 town and refers it to his Ozarkian. I have not yet seen any evidence which makes the 

 separation of the Ozarkian as a distinct system permissible. The Little Falls dolomite, 

 in my view, represents the transgressive portion of the early Ordovicic (Beekmantownian 

 of my classification) which culminated with the deposition of the Tribes Hill limestones, 

 which I consider as essentially continuous with the Little Falls dolomite. During the 

 early regressive phase of the Beekmantownian, beds similar to the Little Falls In lithic 

 character were probably deposited above the Tribes Hill in the Mohawk Valley, but these 

 were eroded during the long interval of exposure between the retreat of the sea in early 

 Beekmantown and its return to the Mohawk region in late Chazyan time (Lowville). 

 During this interval the Tribes Hill was also removed by erosion in the eastern portion 

 of the Mohawk Valley, for it is extremely unlikely that that region escaped Its deposi- 

 tion during the later transgressive stages of early Beekmantown time. I have elsewhere 

 given at length my views on the character of the retreat and readvance, and I have not 

 seen anything in the new facts brought forward since that time to cause me to change 

 them. Indeed, I find that they rather confirm my frequently expressed views In this 

 matter, which are rather widely at variance with those expressed by Ulrich and adopted 

 by his followers. (See my Types of Sedimentary Overlap and Physical and Faunal Evo- 

 lution of North America in Ordovicic and Siluric Time.) 



23 1 hesitate to speak of this fauna as of Arctic origin, for although the Indications 

 are that the present Arctic region was its home, I do not believe that that region had 

 its present relation to the North Pole of the earth's axis. The term Boreal is there- 

 fore chosen to represent this region as being non-committal so far as polar relation is 

 concerned. 



