NIAGARA GROUP. 
89 
in their continuation upwards, are succeeded by a pure crinoidal limestone. So abrupt is this 
change, that specimens can be selected, exhibiting both rocks in connection, as if one deposit 
had succeeded the other instantaneously, allowing no lapse of time and no intermixture of the 
two. 
This is a continuation of the light grey crinoidal limestone which first appears in Monroe 
county, but it has become much thicker and more compact. Near Lockport it is often varie¬ 
gated with red, from the stems of crinoidea which are thus colored. These again lose their 
color, and the mass is grey. At this place the rock is thick bedded, and in regular courses ; 
it is readily wrought from the quarry, and forms one of the best and most durable materials 
for construction which the State affords. It has recently been extensively quarried for the 
enlarged locks upon the Erie canal at this place. 
The following is the character of the different beds, in the descending order, the lowest 
resting on the impure hydraulic limestone. (The numbering is from the lowest upwards.) 
5. Thinly laminated blackish grey limestone, with thin laminae of bituminous shaly matter; the whole 
exhibiting a tendency to a concretionary or contorted structure, and the surface of the layers 
marked by small knobs or elevations as represented in woodcut No. 29. 
4. Greyish brown bituminous limestone, the lower part with irregular cavities containing spar; this 
passes upwards into more regular beds of a dark color, containing few cavities, but marked by 
the presence of blende. 
3. A dark colored limestone, with cavities and veins of spar, often concretionary. 
2. Irregularly thick-bedded limestone of a light grey color, with numerous cavities containing spar, etc. 
1. Encrinital limestone, often beautifully variegated with red; entirely composed of encrinital columns 
and other fossils, which are always broken and worn. 
During the period of the deposition of this limestone, the condition of the ocean seems to 
have been favorable to the production of corals, as is indicated by the immense number 
crowded together in the central portions of the rock. Their partial or entire destruction as 
before described, and their replacement by crystalline matter, renders them a less prominent 
feature than they otherwise would be. Few shells appear to have lived after the deposition 
of the lower strata ; or if they existed, their forms have become obliterated. The broken and 
worn fragments of corals and crinoidea indicate, during the earlier periods, a condition of shal¬ 
low water, as of a coral reef approaching the surface, where the force of the waves destroyed 
all except some of the more solid forms. Subsequently the water seems to have deepened, 
and the comminuted matter, produced by the action of the waves upon the higher portions of 
the reef, settled down in the form of line calcareous mud, enveloping the living corals at the 
bottom. Toward the eastern extremity of the formation all these forms disappear, and the 
limestone is composed of, what we may suppose to be, the finer mud derived from the de¬ 
struction of the corals farther west. The condition, therefore, or the depth of water at the east, 
prevented the growth of corallines; while in the west, all circumstances were favorable to 
their production. 
Geol. 4tu Dist. 
12 
