70 Cherty Lime-rock, or Cornife)-ous Lime-rock. 



burgh, a distance of about ISO miles. It also spreads over a great 

 proportion of the counties of Washington, Rensselaer, Columbia, 

 and the northwestern part of Dutchess. But the underlying ar- 

 gillite is seen forming the bed and sometimes the banks of most 

 of the river, throughout the whole distance ; and in various parts 

 of the four counties mentioned, the argillite is laid bare by the 

 disintegration of the gray wacke. In some places, as at the north 

 end of Beeraft's Mountain, two miles east of Hudson, the gray- 

 wacke is covered with the sparry variety of transition lime-rock. 

 The highest ridges in Rensselaer county are terminated by the 

 rubble or conglomerate of the first gray wacke. Shawangunk 

 Mountain, before mentioned, in Ulster and Orange counties, is a 

 continuation of the same range. But the eastern boundary of the 

 state is mostly uncovered argillite. There are numerous locali- 

 ties, on and near the banks of Hudson River, where extensive 

 beds of siliceous rocks (sometimes called lydian stone) are seen. 

 The rocky bluffs at Hudson city is that stone ; and it contains 

 the same fucoides which are found in the slate quarry of argillite 

 in Hoosick, Rensselaer county. It is also the chief rock at the 

 Troy ferry. 



I will close this paper, which may be the last I shall ever send 

 you, by saying, that the limits between classes seem not to be as 

 well settled among geologists as they ought to be, in the present 

 advanced state of palaeontology. Our red sandstone group has 

 recently been placed among transition rocks by some geologists. 

 Surely the equivalent of our vast corniferous and transition lime- 

 rocks can be found in Europe. If we intend to correspond with 

 Europeans, we ought to agree in the great outlines of generaliza- 

 tion. That our red sandstone group is below our corniferous 

 lime-rock, is surely believed by all who have been at Niagara 

 Falls. That the uppermost transition lime-rock, and the gray- 

 wacke which overlies it, are below this group, is doubted by 

 none who have travelled from Sackett's Harbor to Rochester, 

 along the south shore of Lake Ontario. It may be added, that 

 several species of Cyathophyllum, are very abundant in the cor- 

 niferous rock, and that two or three species of Fungia are often 

 found in the transition lime-rock ; and the red sandstone group 

 lies geologically between the two. 



I here take the liberty to disclaim all partiality for the names 

 I have used for the last score of years in any of my geological 



