56 LOWER HELDERBERG GROUP. 



CHAPTER XVII. 



LOWER HELDERBERG GROUP. 



S 113. This Group wasnamed from the Helderberg Mountains, and defined by 

 Hall in 1859, in the third volume of the Palaeontology of New York. The lower mem- 

 ber is a thin-bedded, often thinly laminated, dark-blue limestone, resting on the Water- 

 lime-beds called Tentaculite limestone. The second member is a thin limestone 

 full of Stromatopora, followed by a dark-gray concretionary limestone, in irregular 

 layers, charged with Pentamerus galeatw and other fossils, which has a maximum 

 thickness in Otsego County of 80 feet, and is called the Pentamerus limestone. The 

 third is a blue, drab-weathering, calcareous shale and blue limestone, full of S/tirl- 

 fera macropleura and other fossils, having a maximum thickness in Albany County 

 of 70 feet, called the Delthyris or Catskill Shaly limestone, from Catskill Creek, 

 near Madison, Greene County. The fourth member is a light-gray limestone, full 

 of broken Encrinites, having a thickness of 25 feet. And above this there is a 

 bluish-gray limestone, charged with Brachiopoda, called the Upper Pentamerus 

 limestone. These local subdivisons are not recognized at any distanoe from the 

 Helderberg Mountains, nor does the Group occur in Western New York or West- 

 ern Canada. Strata of this age occur in two or three small outliers in the great 

 basin near Montreal, at the distance of 200 miles from the nearest exposure of the 

 Group in New York. The most important of these is on the Island of St Helen's, 

 opposite Montreal. The Group, however, is quite largely developed in the Eastern 

 Provinces, where it includes part of the Gaspe limestones. It is exposed on both 

 sides of the Hudson River, and forms the outlier known as Becrafts Mountain, and 

 appears in Maine and New Hampshire. Its maximum thickness in New York is 

 about 400 feet, and nearly as much in Maine, while at Gaspe it is 2,000 feet. It 

 extends southwardly to Tennessee, having a thickness in Pennsylvania of 1,400 

 feet, in Virginia 1,000 feet, in New Jersey 150 feet, and in Tennessee 100 feet. It 

 has been identified at Cape Frazier in latitude 80°. 



§ 114. This is an important Group on the eastern part of the continent, but 

 does not occur west of the Appalachian system, which is in striking contrast with 

 the Onondaga, that spreads out westerly from New York instead of southerly. It 

 abounds in limestone strata, and the evidences of marine life, the latter appar- 

 ently succeeding that of the Niagara age, by gradual change and development. 

 Crinoids, Corals, Bryozoans, Brachiopods, Gasteropods, Lamellibranchs, and 

 Crustaceans were abundant, but we have no evidence that a vertebrate land or 

 fresh-water animal had yet made its appearance on this continent. The evidence 

 of swamp or air vegetation is on the increase, and here we discover the genus 

 Annularia, which subsequently became so abundant in the Coal Measures. The 

 characteristic fossils are : Tentaculites gyracanthus, Spirifera macropleura, S. vanuxemi, 

 Eatonia singularis, E. medialis, Pentamerus galeatus, P. pseudogaleatus, Streptoryhn- 

 chus radiatum, Strophonella punctulifera, Meristella loevis, Bhynchouella semiplicata, 

 R. ventricosa, Strophodonta varistriata, Avicula naviformis, A. manticula, Beyrichia 

 granulata, and B. notata. 



§ 115. Petroleum springs occur on the 8t. John's River and on Silver Brook, 



