4 STRATIGKAPHICAL GEOLOGY. 



The fossils which chiefly characterize the Potsdam Group belong to the 

 genera Palaeophycus, Scolithus, Archaeocyathus ; Obolella, Camarella, Dinobol- 

 us, Lingulella, Salterella, Bathyurus, Conocephalites, Olenellus and Dicello- 

 cephalus. Gasteropoda and Cephalopoda first make their appearance in the 

 Upper Potsdam. Poor specimens of Cystidea and Crinoidea have been found 

 in this Group. 



3. The Calciferous Group, named from the calcareo-silicious character of the 

 rocks. It was called the Calciferous sandrock and Transition rock by Eaton, 

 and the Barnegat limestone, Newburgh limestone, Warwick limestone. Oolitic 

 limestone, Fucoidal layers, and slaty limestone, in the early Geological Reports 

 of New York. It is divided into the Lower and Upper Calciferous Groups. The 

 Upper Calciferous is found in Newfoundland about 1,000 feet in thickness. The 

 Lower Calciferous is the original Calciferous Group of New York. It is ex- 

 posed in Minnesota, Wisconsin, Tennessee, Missouri, Pennsylvania, Virginia, 

 Canada, and other places, usually less than 500 feet in thickness. It is found, 

 however, in Missouri 1,315 feet thick, where it is subdivided into 1st, 2d, 3d and 

 4th Magnesian limestone, and in Newfoundland 1,839 feet thick. The St. Peter's 

 sandstone of the Northwest, named from its great development on the St. Peter's 

 river, belongs to this group. There is in Newfoundland an important series of 

 strata, having a thickness of 2,061 feet, known as division N. of the Newfound- 

 land rocks, which should probably be regarded as part of the Upper Calciferous 

 Group. If so, it would give us a maximum thickness of about 4,000 feet for 

 the Calciferous Group. 



The Lamellibranchiata first make their appearance in this Group, while the 

 Gasteropoda and Cephalopoda become numerous. Pleurotomaria canadensis is 

 known to pass from the Potsdam into this Group. 



4. The Quebec Group, which takes its name from the city of Quebec, in 

 Canada, where it was first studied, and is subdivided into the Levis, Lauzon, 

 and Sillery Groups. The Levis division, which takes its name from Point Levis 

 in Canada, comprehends the Philipsburgh rocks which are 4,860 feet thick, in 

 addition to 1,385 feet of the Orleans section, making the whole division 6,145 

 feet thick. The Lauzon division, which takes its name from Lauzon, in Canada, 

 is about 4,000 feet in thickness. And the Sillery division, which takes its name 

 from Sillery Cove in Canada, is 2,000 feet in thickness, making the maximum 

 depth of the three divisions of this Group 12,145 feet. The Levis division is 

 highly fossiliferous, while only a few fossils are known from other divisions. 

 Some of the fossils of this Group are found both in the Chazy and Calciferous 

 Groups, and the Canadian geologists for a time supposed it to be the equivalent, 

 in some way or other, of these rocks; but later investigations have shown that it 

 has a fauna of its own, and that it offers bed§ of passage from the Potsdam to 

 the Trenton fauna, in addition to those of the Chazy and Calciferous. 



5. The Chazy Group, which takes its name from Chazy, Clinton county. 

 New York, and has an extensive geographical range over New York and Canada, 

 is seldom found over 300 feet in thickness. The upper part of the 1st Magne- 

 sian limestone in Missouri may be the equivalent of this Group, or rather the 

 dark bluish gray semi-crystalline limestones, interstratified with the grayish 

 drab earthy magnesian varieties, destitute of chert, which crop out in some 



