PALEOZOIC TIME LOWER SILUKIAN. 493 



etc., where the Archsean has outcrops not far distant (at Little Falls). A cavity is re- 

 ported to have contained half a bushel of loose, transparent crystals. Fragments and 

 nodules of anthracite coal are sometimes included in the crystals or accompany the crystals 

 in the cavity ; the larger nodules are two inches or more long. Besides quartz and calcite, 

 barite, celestite, gypsum, and occasionally blende are found in its cavities. 



In Canada, north of New York, the Calciferous beds spread widely over the western 

 part of the Ottawa basin, and in general are nearly pure dolomyte, but with cherty or 

 sandy layers. The fossils are mostly weathered out. Thickness, 50' to 300'. In Ten- 

 nessee, the Knox dolomyte, above its lower 2000' of Upper Cambrian, contains typical 

 Calciferous fossils. In Missouri, the first magnesian limestone, which has been ascer- 

 tained by fossils to be Calciferous, has a thickness of 50' to 150'. The Saccharoidal sand- 

 stone, 100' to 133' thick, is very white, and is used for glass-making. 



" Lower magnesian limestone " of Iowa, Minnesota, and Wisconsin, has been found 

 to contain Calciferous fossils in Clayton and AUamaker Counties, according to S. Calvin. 



2. Chazy Epoch. 



At Chazy, according to Brainard and Seely, the Chazy limestone has three divisions : 

 a lower of 310' ; a middle of 265', thick-bedded and abounding in Maclurea ; and an upper 

 of 157', which is very various in character, partly siliceous dolomyte. The middle di- 

 vision contains a 20-foot bed of pure gray limestone which is often oolitic ; it is 50 feet 

 above the bottom, and is free from the Maclurea., — a fact accounted for by the oolitic 

 character, since this structure is produced only in tide-washed calcareous sand-flats or 

 beaches. It makes a handsome marble called "French Gray," while the Maclurea beds 

 make a black or grayish black marble. 



The Chazy beds thin out in the valley of the Mohawk, where the Calciferous is often 

 followed directly by the Birdseye. 



The Chazy is the GrenviUe limestone of the Ottawa region ; it is largely developed 

 about Montreal. It often contains the shells of Lingulse in phosphatic concretions ; and 

 shells of Pleurotomaria occur as casts of calcium phosphate. The beds are 300' thick at 

 the Mingan Islands. No characteristic Chazy fossils have been reported from the Missis- 

 sippi valley. The St. Peter^s sandstone of Iowa, Minnesota, and the adjoining part of 

 Wisconsin underlies the Trenton, and has been referred to the Chazy. It has been re- 

 ported as affording a few fossils related to those of the lower part of the Trenton. But 

 in Iowa and Minnesota the name covers limestone beds as well as those of sandstone. 

 The limestones become thicker in the latter State, and constitute the Shakopee limestone, 

 which is the middle member of the sandstone. In Iowa the St. Peter's sandstone includes 

 also the Willow River limestone, and in Wisconsin the New Eichmond sandstone. A 

 sandstone has been met with, also, in borings in Indiana, below the Trenton, and over 50' 

 of magnesian limestone, which is supposed to be the St. Peter's. The thickness is 150' to 

 224' ; its waters are often saline. 



2. Trenton Period. 



a. Eastern Border region. -^The Hudson beds of Anticosti, along its north side, are 

 of limestone, and 959' thick. Above these are limestone beds of the Upper Silurian, in all 

 about 1400'. The rocks are nearly horizontal. The Trenton occurs in central and west- 

 em New Brunswick, but on the coast and along the shores of Maine only doubtfully at 

 Fo.ster Island near Machiasport. 



b. Appalachiun and Interior Continental regions. — The Trenton limestone in central 

 New York extends as a surface rock through Oneida and Lewis counties to Lake Ontario ; 

 then reappears across the lake and stretches westward in a band 30 miles wide to Georgian 

 Bay. It occurs also on the Manitoulin Islands and Drummond's Island, Lake Huron. The 

 thickness at Montreal is 600', in the Ottawa basin as great, and nearly 1000' west of 



