DESCRIPTIONS OF THE FORMATIONS. 17 



member, as the order is now understood, is 1,839 feet thick, of black graptolitic 

 slates. The Quebec group, however, presents somewhat different characters 

 in various parts of its distribution. The districts where it is developed are 

 characterized by great faults and inversions of the strata, rendering, as appears 

 above, even their order uncertain. 



Dr. Hunt, in his table of formations, places the Sillery below the Potsdam and 

 Calcif erous, and the Levis above them, including in the Levis alike the graptolitic 

 slates, the Lauzon, and the fossiliferous limestones of the Levis of Logan. The 

 Quebec group extends along the west side of the Green Mountain range, and covers 

 a considerable part of the State of New York, east of the River Hudson, the rocks 

 being part of the non-fossiliferous clay-slate formerly called the Hudson River 

 slate, which outcrops near Poughkeepsie. The area is divided, on the west, from 

 the true Hudson-River slate formation by the great fault mentioned in note 8 of 

 New York. 



3 c. Chazy. To the Quebec group succeeds the Chazy limestone. As 

 a whole, it is a dark, irregular, thick-bedded limestone. At Chazy, New York, on 

 Lake Champlain, it contains many rough, irregular, flinty or cherty masses. At 

 Essex the beds are more regular, and form, in consequence, a better building stone. 

 As a limestone it is purer than the Calcif erous, being non-magnesian ; the principal 

 foreign matter is silica in the form of chert. It is free from the brown earthy spots, 

 and the masses of brown calcareous spar so common in the Calcif erous sandrock. 



This formation is 130 feet thick on Lake Champlain, but it is less constant in 

 the series than the others, and as it is not an important formation on the lines of 

 the railroads, an extended description is not here necessary. It is not found in the 

 valley of the Mohawk. Its fossils are found in Pennsylvania and Virginia, but its 

 limits are not there defined. In the Northwestern States the St. Peter's sandstone 

 occupies the same place in the series as the Chazy in the east. 



3 c. St. Peter's Sandstone, (Upper Sandstone of Owen). This is a western 

 formation and does not occur in the Eastern states, but Prof. Lesley thinks it 

 may have representatives in the massive silicious members of the great limestone- 

 mass of from 5,000 to 6,000 feet thick, as measured along the two branches of the 

 Juniata in Pennsylvania. It is first recognized in going west, to the southwest of 

 Winnebago Lake. It is also seen up the Mississippi, near St. Paul and St. Anthony, 

 and on the streams of northeast Iowa, and at La Salle, Illinois, where it is brought 

 to the surface by an anticlinal axis. ^ It is remarkable for its uniform thickness, 

 which is from 72 to 100 feet over a space of 500 miles in length and 400 miles in width. 

 In Central Wisconsin, however, its thickness is very irregular. It is also of the same 

 character throughout, being composed of wonderfully uniform and exceedingly 

 minute grains of sand, held together by the merest trace of cement, so that the mass 

 may easily be moved with shovel and pick, as is everywhere done for the purpose 

 of obtaining sand for mortar. This sandstone, though usually white, sometimes 

 assumes a buff or brown color from the presence of iron, and in some localities 

 it becomes red or is marked by bands of a bright green color. It appears like a 

 recurrence of the Lower or Potsdam sandstone. Being composed almost entirely 

 of pure silica it is, when not colored by oxide of iron, one of the very best 

 materials yet discovered in the west for the manufacture of glass. It is the 

 same as that known in Missouri as saccharoidal sandstone, which is carried to 

 Pittsburg, Pennsylvania, and used by the glass-makers in manufacturing the best 

 kinds of glass. See Note 2, Missouri. 



