284 The American Geologist. November, 1901. 
needles of celestite, and the abundance of small spherules of 
marcasite. In the lenses themselves cavities filled with g-ypsum 
in four or five pound masses are common. At Niagara several 
of these cores have been found weighing from ten to fifteen 
pounds. [PL xxix, Fig. 6.] 
The rock is apparently a structureless, exceedingly com- 
pact, dolomitic limestone, breaking with an imperfect con- 
choidal fracture. In color grayish blue, it weathers, like the in- 
cluding beds, to a light brown or yellowish hue. 
Only by weathering is the true character of these masses 
clearly brought out, and a satisfactory explanation of their 
origin made possible. Then they prove to be mainly composed 
of a remarkable development of fistuliporid and other bryozoan 
forms, and to contain unusual accumulations of cephalopods, 
trilobites and brachiopods. Many of the species are rare or 
imknown in the surrounding limestone. 
The lenses of Rochester alone have yielded, exclusive of the 
Bryozoa, which will probably add very materially to the num- 
ber, sixty-eight genera, ninety-nine species and two varieties, 
disposed as follows : 
Class. Genera. Species. Variety. 
Sponges 2 2 
Corals 3 5 
Crinoids -4 4 
Cystids 1 1 
Tubicolons Annelids 2 2 
Brachiopods 29 36 
Pelecypods 5 9 
Gasteropods 5 7 
Cephalopods 3 8 
Ostracodes 1 1 
Trilobites 9 10 2 
Total 68 99 2 
PREVIOUS OBSERVATIONS. 
This phenomenon was observed by Dr. Eugene N. S. Ring- 
ueberg,* in Orleans and Niagara counties in the vicinity of 
Lockport and Gasport. He found them in restricted areas and 
of extremely variable thickness, appearing to be limited to the 
capping plane of the Clinton upper limestone. In view of the 
irregular and undulating appearance of the upper surface and 
*The Evolution of Forms from the Clinton to the Niagara Group." Am. 
Nat., September, 1882, p. 711. 
