NIAGARA LIMESTONE. 369 



taneously. The view that best explains these facts is, (1) that the 

 mounds and ridges were ancient reefs, and (2) that the granular sand 

 rock was formed from calcareous sands, derived by wave-action from 

 the reef, and (3) that the compact strata originated from the deposit 

 of the finer calcareous mud that settled in deeper and more quiet 

 waters, the whole process being analogous to, if not identical with, the 

 coral formation of the present seas. But before pursuing this analogy 

 farther, it will be well to consider the evidences of life found in these 

 rocks. While some of the reefs, or at least that portion of them that 

 happens to be exposed to examination, present only a few fragments 

 of fossils, others are prolific in organic remains, and some of them are 

 remarkable for the richness and variety of their fauna. The reef near 

 Wauwatosa (Schoonmaker's quarry), is a striking instance of this. 

 There have been collected from it, chiefly by Dr. Day, probably not 

 less than two hundred species. Of these there have been identified 

 28 Corals, 8 Bryozoans, 4 Crinoids, 19 Brachiopods, 11 Gasteropods, 

 9 Lamellibranchs, 24 Cephalopods, and 16 Trilobites. And an ex- 

 haustive examination of the collections would doubtless much increase 

 the number. The specific character of these will be seen by consult- 

 ing the accompanying table. This locality is especially notable for 

 its Trilobites. At the quarry in Milwaukee, Corals are proportion- 

 ately more abundant in number of individuals. At Noessen's quarry 

 near Saukville, where there is a mingling of Racine and Guelph 

 faunas, some portions of the rock are little more than a mass of coral 

 remains imbedded in calcareous sand. 



Of the granular varieties of rock, that which is nearest allied to the 

 reef rock is peculiarly notable for an abundance of Crinoids. The lo- 

 cality near Racine is preeminent in this respect. Upwards of thirty 

 species have been identified from this one locality. These are associ- 

 ated, as will be seen by consulting the table, with a large number of 

 Corals, Brachiopods, Gasteropods, Cephalopods, Trilobites and a lesser 

 number of other forms. Very similar faunas are displayed at Green- 

 field, Waukesha, and elsewhere. The more purely granular sandrock 

 seldom contains many fossils. 



The fauna of the compact strata is distinguished for the conspicu- 

 ous presence of the straight and curved Cephalopods with compara- 

 tively few associates. The Cephalopods are abundant, as already 

 noted, in the reefs and crinoid beds, but are overshadowed by the 

 number and variety of other forms, while in the compact rock, they 

 greatly predominate. 



It appears then, (1) that upon the reefs there swarmed a vast variety 

 of life; (2) that upon certain banks or shoal areas there was also great 

 Wis. SUE. 24 



