1>^70.] 411 [Winchell, 



epoch to wMch tliey belong. They are the exceptions, lohich do not derange 

 the general symmetry.''^ 



Let us now examine, for a moment, the circumstances wliicli afford a 

 shadow of plausibility to the extraordinary dogma of the parallelism of 

 the Chemung- and Marshall groups. It is alleged first, that the fauna of 

 the Chemung assumes gradually a less Devonian and more Carboniferous 

 aspect, when traced westward within the limits of the State of Nevv^ York, 

 and that it is possible that the characters of the Marshall groujp would be 

 reached in the prolongation of the Chemung through the Western States. 

 This allegation must be considered in the light of the fact, that a great 

 thickness and geographical extent of strata in eastern New York, which 

 were, a few years since, regarded as belonging to the Catskill group, are 

 now pronounced by Professor Hall and Col. Jewett to be really a part of 

 the Chemung; and that strata which were formerly regarded as Chemung 

 belong really to the Hamilton. Restoring to the Hamilton that wliich is 

 its own, it cannot be otherwise than that the Chemung strata of eastern 

 ISTew York should present a more modern aspect than was once supposed. 

 But let it be granted that even ypt the Chemung presents a more Carbon- 

 iferous aspect in western than eastern New York, it is not yet a Carbon- 

 iferous fauna ; it retains numerous Devonian types ; it does not embrace 

 a trio of species, if it does a single one, which reappear in central and 

 eastern Ohio. All this is unprecedented in formations of the same age, 

 at points but one or two hundred miles removed from each other. 



In the next place, some local difference in the nature of the sediments 

 is admitted to exist. The rocks of the Marshall group, both in Ohio and 

 Michigan, embrace a bed which is somewhat calcareous ; in southern In- 

 diana they are known only by an aluminous limestone ; iu Illinois and 

 Missouri they are, to a considerable extent, calcareous and argillaceous. 

 On the other hand, it is notorious that the great mass of the Marshall 

 group consists of olive, reddish and yellowish sandstones, and shaly sand- 

 stones, which can scarcely be distinguished from the strata of the Che- 

 mung. The rocks are, identical, and so far as we have the means of 

 judging, the physical conditions under which the sediments were accumu- 

 lated, must have been extremely similar. We discern none of those 

 changed conditions which are always present on the occurrence of a loca^ 

 fauna. And yet the two faunas are more distinct than those of the Por- 

 tage and Hamilton — vastly more distinct than those of the Hudson Eiver 

 and Trenton groups. Such i^retensions are not set up in i-eference to any 

 other formation. Lingula prima, of the Potsdam group, is recognized in 

 the coarse sandstones of New York and Minnesota, and the fine alumi- 

 nous shales of Alabama. The western prolonga,tion of the Hudson River 

 group is stocked with the same Bhynchonella increbescens, Orthis lynx, 

 Strophomena alternata and Ghatetes lycoperdon, as the typical strata of 

 eastern New York. The various physical conditions under which we find 

 the Niagara group, present us uniformly with Canyocrinus ornatus, Ha- 

 lysites eutenularia, Favosites Gothlandica, Athyris nitida, Spirlfera radiata, 



