MEDINA SANDSTONE, CLINTON AND NIA&ARA GROUPS. O 



When we examine the Clinton group in the central part of the State, its analogies are chiefly 

 with the Medina sandstone ; and it is there a powerful and important formation, presenting, 

 however, great variation in its successive beds, and characters in every respect truly protean. 



In its western extension, the Clinton group assimilates in character to the Niagara group, 

 and, in the Westej-n district, has nearly lost the character which it presents in Oneida covmty. 

 At the same time that the group assumes a more calcareous character in its western extension, 

 it loses the fossils which were typical of it, and becomes charged with fossils peculiar to 

 calcareous strata. Thus while we find its lower beds, from Wayne county westward to the 

 Niagara river, characterized by peculiar fossils, we find the upper beds containing many species 

 which pass upwards into the Niagara group. Indeed there is no line which can be designated 

 between these two groups, which shall mark the limits of the organic products. It is true, 

 nevertheless, that by far the greater part of the fossils of the two groups are distinct ; and the 

 small number in the lower group, of those which we regard as proper to the Niagara group, 

 are for the most part inconspicuous, and not so well developed as they are in the Niagara. 



To ascertain the value of these characters, and to decide the relations of these groups, has 

 cost much time and labor ; and the localities, with their productions, have not yet been fully 

 explored. In these investigations some new facts have been brought to light, facts which all the 

 previous examinations had not shown. Among these I may mention as pertinent to the present 

 object, the discovery of several species of fossils heretofore known only in the lower rocks. In 

 the western part of the State, the lower beds of this group have furnished very dilapidated 

 specimens of Bellerophon bilobatus, with Delthyris lynx, and one or two imperfect specimens 

 of a Leptcena undistinguishable from L. alternata. A few other fragments and imperfect speci- 

 mens have also been found, which appear to be of forms belonging to lower silurian strata. 

 These facts are extremely important and interesting ; and I take the first occasion of recording 

 them, from the circumstance that all our investigations previously had only strengthened the 

 opinion that no fossils of the lower rocks had passed the Oneida conglomerate. Neither should 

 it be forgotten at the present time that all the specimens found are in a very dilapidated con- 

 dition, and the number altogether so few, that we might even yet be disposed to doubt whether 

 the same lived at this period, or whether their appearance here is merely accidental. 



In its western extension, the upper limit of the Clinton group is marked by a thick bed of 

 limestone, which contains several species of fossils common to this bed and the group above, as 

 well as several which are peculiar to the Clinton group, and do not pass above this limestone. 



The Niagara group, which is so well marked and powerful in the neighborhood of Niagara 

 Falls, Lockport, Rochester and even in Wayne county, becomes diminished in thickness in its 

 extension eastward, and appears quite subordinate to the Clinton group. The fossils peculiar to 

 the Niagara group farther west are scarcely recognized ; and in Oneida county, this group is in 

 some places represented by a thin mass of shale, with some beds of concretionary limestone. 

 In this condition it appears scarcely separable from the Clinton group which it succeeds, and, 

 in the early part of the Geological Survey, was included with it under the name of the Protean 

 group. Diminished and inconspicuous as the Niagara group has thus become, even in the central 



