1886.] NATURAL SCIENCES OF PHILADELPHIA. 41 



nated mass has sometimes grown as an incrustation of a central 

 nucleus, a shell or coral ; other times it forms a more or less thick 

 expansion with a small point of attachment, and otherwise a free 

 underface covered b}^ a wrinkled dense epithelial crust." 



After this, in a general way correct description, they discuss 

 the original nature of the hard structures of Stromatoporoids, 

 which in fossilized condition are found calcareous, other times 

 siliceous, or partially calcareous and partially siliceous ; and demon- 

 strate the originally calcareous nature of the ske.eton of Stroma- 

 topora particularly by the circumstance that the specimens of 

 Stromatopora are always found in a calcareous condition, when 

 the associated fossils are likewise calcareous ; but if the associated 

 primitively calcareous fossils are to any large proportion silicified, 

 then also the skeletons of StromatojMra are found more or less 

 completely silicified. The various modes of preservation are 

 then enumerated : a, skeleton wholly calcareous ; 6, skeleton 

 calcareous, interlaminar spaces infiltrated with silica ; c, skeleton 

 silicified but the interlaminar spaces infiltrated with calcite ; d, 

 both former conditions of preservation represented in one and the 

 same specimen ; e, both skeleton and interlaminar spaces trans- 

 formed and filled with silica. 



Entering into description of the more minute particulars of the 

 structure of Stromatopora the writers state that of the before- 

 mentioned pillars not all reach from lamina to lamina, but that 

 rudimentary shorter ones occur between. The pillars and laminae 

 are represented as composed of granvilar carbonate of lime, which 

 shows no structure, except occasionally an indistinct indication 

 of reticulation. According to my own observation, in all well- 

 preserved calcareous specimens of Stromatopora, the substance 

 of the laminae and of the pillars, being composed of a network of 

 interwoven delicate fibres, can be recognized with the greatest 

 distinctness, with a good simple lens, although not so distinctly 

 with the higher powers of a microscope, both the organic structure 

 and the crystalline mineral structure then becoming visible, thus 

 causinsr a blurred image. 



The pillars are described as either simple rounded prominences 

 or else as vermicular and anastomosing crests which are imperfor- 

 ate, solid, not tubular. The writers, however, observed on the 

 surface of weathered silicified specimens sometimes a part of the 

 exposed pillars perforated by a central opening, which they try 



