This limestone is the repository of the beautiful spars found at Lockport and Niagara Falls; and the shale below it is filled with beautiful organic remains. When we pass westward this rock becomes metalliferous in the highest degree, containing all the productive lead mines. of Illinois, Wiskonsan and Iowa.

The accompanying illustration, Pl. XI., presents some of the trilobites which are found at Lockport. They are apparently identical with fossils of the Wenlock shale in England. Although most abundant at Lockport, still many of them may be seen at Rochester, and at Wolcott. The shells of Plate XII, are more widely distributed, and occur at Lockport, Rochester, Wolcott, and numerous intermediate places. The singular and beautiful fossils known as Encrinites, are more abundant in this group, than in any other within the State. We have hardly space to present some of their singular and beautiful forms. Some of the species are abundant at Lockport, but are rarely found east or west of that point. (See figures Pl. XII.) Among the common form of corals in the shale, are those on Plate XIII., and in the limestone the Catenipora is very abundant in nearly all localities. Numerous other forms might be presented, but we can only glance at what has been done, and refer our readers to the volumes themselves.

The Onondaga salt group, which follows the Niagara group, is one of the most important in all the series in New-York All the copious brine springs of the State, have their origin in these rocks, the extent and development of which have been pointed out, so that borings and excavations can be undertaken with a knowledge of their position. Allusion has already been made to the facts ascertained during the survey, in relation to the position of the strongest brine.*

Besides the salines, this group of rocks is important as furnishing all the gypsum of importance within the State; and this article alone may be regarded as of more pecuniary value than all the gold mines in the Union. The range and extent of the rocks furnishing gypsum or

* It may not be out of place here, to notice an opinion which prevails among some at least in relation to salines. Some very weak brine springs in the southern part of the State, or some places where tradition informs us that the Aborigines manufactured salt, are believ ed by the inhabitants to be as capable of producing brine as the salines of Onondaga, and they therefore blame the Geologists for neglecting them. All such persons, may rest assured that whenever any apparent neglect has occurred, they were satisfied from the Geological position that no important saline could exist; and though such rumor may promise much, the in habitants of New-York dan never look to the country south of the Onondaga salt group for even a moderate supply of salt.