NIAGARA GROUP. 



109 



CORALS OF THE NIAGARA GROUP. 



This group of strata, though of very moderate thickness, contains nearly or quite as many 

 species of corals as all the preceding groups together, excluding the graptolites. This increased 

 number of species has not been procured either by the exploration of larger tracts, or of more 

 numerous localities, than in the lower strata ; but, on the contrary a smaller area has been 

 examined, and a fewer number of localities. Indeed nearly all the species described under this 

 group have been found at Lockport and vicinity, while many other localities afford a large 

 proportion of the whole number, and perhaps diligent search would discover still more. The 

 excavations for the enlarged Erie canal at Lockport have brought to light several species in 

 shale, which, by ordinary excavation and the process of weathering, would not have been dis- 

 covered. The rapid disintegration of the shale on exposure soon destroys all except the more 

 solid calcareous corals ; and the Bryozoa, which are more prolific in these shales than else- 

 where, are usualy obliterated, or so much injured as to render their recognition difficult. In 

 the lower part of the limestone, however, myriads of the smaller branching corals are pre- 

 served, and likewise some of the more solid or hemispheric forms. Still higher, those massive 

 forms occur which leave on their destruction large cavities,- or become changed to crystalline 

 matter by the action of sulphuric acid waters. 



It is not only the great number of species here displayed which renders the period ex- 

 ceedingly interesting, but, also, in a higher degree, the great number of new types which, for 

 the first time in our knowledge, came into existence at this epoch. Another fact, also, of impor- 

 tance in its geological bearing, will be made manifest in our progress in the study of these 

 corals ; and that is, that they are really as typical of the strata in which they occur, as are the 

 fossils of a higher organization. In all these forms we do not yet recognize a single species of 

 the Lower Silurian formations ; while, on the other hand, scarcely one of these prolongs its 

 e.xistence into the succeeding period. Even the smaller Bryozoa of this and the higher strata 

 are quite distinct. 



In the family of Cyathophyllidea, which in the lower rocks of our State is represented only 

 by the genus Streptelasma, we have at least four new generic types introduced at this period. 

 In the Favositidea, the genus Favistella of the lower rocks is apparently represented by 

 another generic form, and the true Favistella is unknown. Thus far, I am not able to decide 

 positively that the Genus Favosites occurs at this period ; and all the corals heretofore re- 

 ferred to that genus evidently belong to a different one. The smaller forms, like Ch.etetes, 

 have in some examples stellate cells, showing a different relation to those from the lower rocks. 



The genus Heliolites, in one or more species, characterizes the strata of this period, not 

 only in New- York, but far to the westward ; while the Catenipora eacharoides is preeminently 

 characteristic of the group. This genus appears for the first time in the Clinton group, but 

 only becomes developed in a high degree in the Niagara limestone, which in New-York con- 



