BLACK-KIVER LIMESTONE. 47 



CORALS OF THE BJRDSEYE AND BLACK-RIVER LIMESTONES. 



Plate XII. 



80. 1. COLUMNARIA ALVEOLATA. 



Pi,. XII. Figs. 1 a, b, c. 



Columnaria alveolata. Golxifuss, Petrefacta, pag. 72, tab. xxiv. fig. 7 a, b, c. 



— — Eaton, Geol. Text-Book, pag. 131, pi. 4. 



Columnaria. Emmons, Geol. Report, pag. 276, fig. 2. 



A hemispherical or irregularly massive coral, consisting of radiating, parallel or diverging 

 tubes ; tubes hexagonal (or varying from 5- to 7-sided ), striated longitudinally, crossed by 

 transverse dissepiments with vertical radiating lamellae ; no communicating pores. 



The vertical lamellae converge from the sides of the cell towards the centre, but I have 

 not yet seen a specimen in which they meet at the centre. These lamellae are unequal in 

 number, varying apparently from twenty to thirty, and never meeting in the centre in our 

 specimens : they are often partially obliterated, and leave the inside of the tube marked 

 only by sharp ridges, corresponding to the striae upon the outside ; when the transverse 

 dissepiments are also obliterated, these ridges are denticulated, marking the point of 

 junction. The vertical lamellae are only visible in weathered specimens, as fig. 1 b, where 

 the ends of the tubes are exposed. In a large number of specimens, the radiating lamellae 

 are entirely obliterated, and the dissepiments only preserved, as in fig. 1 a. These are 

 common at Watertown, Jefferson county. In the Mohawk valley and elsewhere, when 

 preserv^ in compact limestone, the tubes are solid, separable from each other, end 

 preserving very perfectly their deeply striated surfaces, as in fig. 1. 



The coral occurs in hemispherical masses, varying in diameter from three inches to 

 several feet.* 



Fig. 1. A vertical section of a compact specimen, showing the striated walls of the cells. 



Fig. I a. A vertical section, showing the transverse dissepiments, with the vertical lamellae obliterated. 



Fig. 1 b. A transverse section (weathered surface), showing the radiating lamellae. 



Fig. 1 e. The same enlarged. 



Position and locality. Glensfalls ; Chazy ; Watertown ; Lowville, Lewis county ; Am- 

 sterdam and numerous other places in the Mohawk valley, always confined to the Black- 

 river limestone, and is never known to rise above it in any locality. In many situations, it 

 forms a large portion of a single thick stratum near the termination of the rock, 



• There ig a specimen (a portion only of an entire mass) in the State Collection, weighing about 1500 pounds : the 

 whole mass probably weighed 2000 or 3000 pounds. This specimen is from the Mohawk valley, and was blasted from 

 the rock in quarrying stone for the enlarged Erie Canal ; and I am indebted to the Engineer, Mr. M'Alpin, for being 

 able to place it in the Collection. Certainly, when we find at so early a period such masses of coral, there is no reason 

 why extensive coral reefs may not have margined our early shoals or islands of granite, as those of modern origin do 

 the iilanda and shoals of oar present seas. 



