ORIGIN OF CARBONATE IN CORALS. 271 



We have collected a scries of specimens from the locality producing 

 the types (Phelp's quarry, Alpena, Michigan), and from these have been 

 al )le to learn something further in regard to the internal structure. The 

 septa are made up of superposed layers, convex upward, as in C. mag- 

 nificum, but they are coarser and more distant in proportion to the size 

 of each septum. They are also flatter, being less deflected at their edges. 

 In specimens in which they could be satisfactorily counted they average 

 from 15 to 20 to the cm and occupy a corresponding position in neigh- 

 boring septa as though deposited simultaneously. The supporting 

 growths are present, rising vertically through a series of the septal layers. 

 The interseptal cavities are narrower and less distinctly defined than in 

 type forms. We were unable to find a radial section clear enough to 

 show defined vesicles in the outer area, but toward the center they come 

 into view as the transverse leaflets between the contorted septa, taking 

 the place of true tabulae. 



There are several considerations which lead to the conclusion that the 

 solid deposits of carbonate' could not have been made by the polyps 

 themselves : 



1. Some of the associated fossils are filled in just as completely with 

 material indistinguishable from that of C. ponderosum. The best example 

 is that of Strombodes alpenensis, Rom. Numerous corals and crinoid 

 stems were collected, showing a similar structure but in which the de- 

 posit was less compact and hence softer. A colony of Acervularia with 

 a height and diameter of about ten feet showed patches and layers of 

 this material nearly or quite obscuring the structure. 



2. That these deposits did not take place directly in the inhabited 

 calyx is evidenced by the layered structure and supporting growths. 

 From the lower abandoned portions of the corallum the polyp was, in 

 the main, completely shut off by septal layers and dissepimental struct- 

 ures. 



3. The process would have been uneconomical and highly wasteful of 

 building material. So far as we can see, it would have been of no special 

 value to the polyp. Solid deposits may be found in some modern, 

 delicately branching corals, evidently for the purpose of strengthening 

 them, but no such use could be assigned in the case of a simple, turbi- 

 nate form. 



4. Spherulites, corresponding in appearance and structure with '"'or- 

 bicular silica, 1 ' were found imbedded in this solid deposit of a specimen. 

 They were numerous about the calyx, and on eating away the under side 

 of the specimen with acid they were revealed in still greater numbers, 

 along with crystals of iron pyrites. Each spherule consists of a rounded 

 lindens of silica, whitish and opaque to the eve, but crystalline in struct- 



