ART. 21 OEDOVICIAN TRILOBITES — ULRICH 55 



a part, and in Europe usually only a small part, of the total time 

 involved. This conclusion applies to the whole of Ordovician time 

 and to invasions of very different northern and southern faunas as 

 well as those that were at home in the Middle Atlantic. Europe, par- 

 ticularly northern Europe, seems to have only graptolite-bearing 

 shales of Athens age to represent the great accumulation of marine 

 deposits included in the Blount group in east Tennessee and south- 

 western Virginia. Middle Chazyan seems to be represented in the 

 Girvan District of Scotland but can not be positively recognized 

 elsewhere in Europe. The OrtlioceroLs limestone of Norway, Sweden, 

 and the Baltic region may correspond to our Lower Chazyan, but, 

 for reasons than can not be readily given at this time, I am inclined 

 to correlate it with some part or parts of our Buffalo River series. 

 Should this belief be substantiated there would be little or nothing 

 left in Europe to set opposite our Lower Chazyan. And so it goes. 

 North America has many Lower Paleozoic formations that at best 

 are weakly represented by sedimentary marine deposits in Europe, 

 whereas those in Europe seem in most cases not strictly correlatable 

 with ours. Their time relations seem to interfinger. 



Another important factor that may be largely responsible for 

 some of our difficulties in understanding and properly correlating 

 European formations with those in America is the probability that 

 the prevailing correlations that are carried from one to another of 

 of the European exposures of Lower Paleozoic deposits are seldom 

 strictly correct and often decidedly in error. In America we have 

 proved that because of oscillation of the surface of the continent 

 and the shallowness of the marine invasions the successive deposits 

 in the varying Appalachian troughs and basins and in the broader 

 basins of the interior areas are but seldom on the same stratigraphic 

 plane. In other words, the bodies of water in which the deposits 

 were made were patchy and often shifted from one negative area 

 to another, thus being much less extensive at any particular time 

 than was believed formerly. Most probably very similar conditions 

 obtained in Europe also. Indeed, after seeing most of the Scandina- 

 vian and British exposures of early Paleozoic rocks, I am thor- 

 oughly convinced that the epicontinental seas in which they were 

 laid down were localized and shifted about from time to time in 

 essentially like manner and frequency as we have every reason to 

 believe they were in America. Naturally, then, the sequences of 

 deposits and of the times represented by them in each of the several 

 areas in which negative tendencies are dominant vary more or less from 

 place to place. If the European geologists in studying their Paleo- 

 zoic deposits will stress differentiation of the beds and fossils of 

 different basins, rather than continue to emphasize their points of 



