294: Eepoet of the State GEOLoaiST. 



quite striking. Some specimens are readily separated into thin 

 sheets or latilaminae. In others, more completely infiltered by 

 calcite or less weathered, the latilaminse are indicated only by 

 darker and lighter bands. When in this condition they are not 

 disjoined by a blow from the hammer, but the specimen chips or 

 fractures like a structureless limestone. Surface characters are 

 best studied under the former condition of preservation. Sections 

 of many Helderberg Stromatoporoids examined show that the 

 original calcareous skeleton of the colony has been replaced by 

 some dark material, probably impure limestone, while the spaces 

 between pillars and partitions are filled by transparent calcite. 

 The definition is nearly always indistinct. 



Tangential sections do not remain parallel to the surface in 

 this species, except over small areas, for the curvature is not 

 regular but flexuous, and the latilaminae are more or less 

 foliaceous and imbricating. Thus extended sections cut the 

 frequent monticules at all angles and appear like panels of curly 

 maple. 



In specimens which break along the latilaminaB the surface 

 is seen to be vermiculate and porous, thickly covered with 

 prominent conical elevations. This characteristic vermiculate 

 structure is shown also in tangential sections, and is not due to 

 weathering and preservation. Astrorhizae are numerous, but 

 small and inconspicuous, as if they were merely the usual porous 

 structure intensified. They are distributed over the surface, and » 

 are often to be found on the sides of the monticules. The 

 monticules, as shown by radial sections, are usually superimposed 

 throughout one latilamina, but in two consecutive latilaminae 

 this may or may not be the case. They are often pierced by 

 straight central canals directed radially. These canals often 

 extend through one whole set of monticules. They have no 

 proper walls and, therefore, cannot be referred to " Caunopora " 

 tubes or tubicolous annelids. When broken transversely the 

 mamelons are seen to be distinctly porous. The pores, or canals, 

 are often arranged in concentric series, coincident with the cut 

 edges of the intersected laminae, and evidently represent sections 

 of the astrorhizal canals. 



Weathered fractures and properly oriented sections show that 

 the radial pillars are strong, parallel, and continuous through 



