GEOLOGY OF STEEPROCK LAKE. 15 



normal to the axis of the organisms. In oblique sections the peri- 

 phery may be more or less elliptical. The diameter of these circular 

 boundaries varies in the hundreds of specimens observed, from about 

 1 inch to about 15 inches. This variation in size is probably due 

 partly to differences in the stage of development of the organism, 

 and partly to the position of the random section of the surface of 

 the limestone exposing the form. For when viewed in three dimen- 

 sions and not merely in section, some of these fossils appear to have 

 a tapering and more or less curved or- cornucopia shape. The radial 

 structure is due to the presence of rays which diverge from the axis 

 of the cornucopia. Occasionally, it may be observed that these are 

 interrupted by one or m.ore cylindrical or conical septa concentric 

 with the axis of the cornucopia, but in most cases no such concen- 

 tric septa can be detected In other cases, particularly in regard to 

 the larger forms, it cannot be observed that they are cornucopia 

 shaped, an'! the rays appear to radiate in all directions from a 

 centre. 



Often these fossils are so crowded together that they abut one 

 against another; but in no case are the individual rays observed to 

 cross. In the larger fomis the limits of the radial structure are much 

 less definite than in the case of the smaller cornucopia shaped forms, 

 and on the weathered surface the rays appear to fade away into the 

 general matrix of limestone. The clearly apparent structure is, 

 however, contained within a circular area on the surface of the 

 rock. 



Where these forms have been silicified they commonly project 

 prominently above the surface of the limestone, and the structure 

 can be more easily observed. In these silicified forms the rays and 

 the tapering or cornucopia shape are commonly apparent. It is 

 evident from the sudden passage from conglomerate to limestone 

 and from the cross-bedded character of some of the limestone, that 

 the organisms which contributed their remains to the building up 

 of this important formation thrived in shallow water, and that the 

 accumulation of their structures gave rise to some sort of a fringing 

 reef along the shore, which from time to time was reduced by the 

 waves to a calcareous sand which was scoured by the currents. 



The fossils collected were submitted for study to the Hon. 

 Charles D. Walcott, the eminent authority on the earliest forms of 

 life, and he has very kindly supplied the descriptive notes which 

 follow. 



