Classes of Rocks. 153 



port Hill. Cdlciferous grit overlies the slate in grit-like 

 blocks. It is used in the construction of locks and aqueducts 

 at Jordan and other places. It abounds in shells. Varieties. 

 Conchoidal. This variety breaks into conchoidal or lentic- 

 ular forms. It appears in the bed and on the banks of the 

 canal in Minden, where it contains petrifactions resem- 

 bling the chiton. Argillaceous. This is common through- 

 out. Shell grit occurs near, or at the upper surface of the 

 stratum. Contents. Gypsum, water cement, and the ver- 

 micular limestone are found in beds in this rock and in no 

 other. All may be seen at Manlius Centre, along the south 

 bank of the canal. Shell limestone is common in this stra- 

 tum. One of the best localities is between the lower Gene- 

 see Fall and the one next above it, on the west side. 



17. Geodiferous Limerock. 



Subdivisions. Swinestone is found in the bed and banks 

 of the Erie canal near Genesee river, and extending one 

 mile east. The canal at Lockport is cut through this rock 

 to the depth of nearly thirty feet for two miles. It forms the 

 upper part of Niagara Falls to the depth of seventy feet. The 

 sandy division overlies the swinestone, is less fetid, somewhat 

 stratified, and contains quartzose grains. Its characters are 

 well exhibited at Black Rock, immediately under the corni- 

 tiferous limerock. Varieties. The Fetid can scarcely be 

 considered a distinct variety. The darker the color, the 

 more fetid the odor. Contents. The geodes contain sul- 

 phate of strontian, granular gypsum, laminated selenite, 

 anhydrous gypsum, fluor spar in limpid cubes, arragonite, 

 dog-tooth spar, brown spar, and waxy blende. Galena 

 has been found in small masses imbedded in this rock, and 

 Bitumen has been observed in exudations upon its surface. 



18. Cornitiferous Limerock. 



Subdivisions. The lower or compact side contains layers 

 of hornstone, generally in pairs, often of great extent. The 

 upper, or shelly side, contains irregular masses of hornstone, 

 often somewhat nodular. Black Rock affords an excellent 

 locality of the compact, and Auburn, behind the state prison, 

 presents a most perfect locality of the shelly. 



Vol. XIV.— No. 1. 20 



