1886.] NATURAL SCIENCES OF PHILADELPHIA. 45 



of considerable thickness, and are separated as usual by well- 

 marked interlaminar spaces, but the latter are quite open, and 

 there is a total absence of the vertical calcareous pillars which 

 occur in the normal Stromatoporoids; but the whole mass is per- 

 forated by innumerable vertical canals, which are destitute of 

 walls, and open directly into the successive interlaminar spaces 

 which they penetrate, as well as into open irregular laminae in 

 the general laminated skeleton." 



This is an erroneous conception of the structure of that famil}^ 

 as these supposed tubules are in reality casts of actual solid 

 tissue pillars which vertically intersect the laminated mass, some- 

 times without interruption in the different intersected layers, 

 sometimes in each band (consisting of a group of subordinate 

 delicate layers), these pillars start anew from a fresh basis. 



The ordinary mode of preservation of the fossil has generally 

 impaired the original organic texture of the skeleton, which 

 became almost totally destroyed, and the space occupied by tissue 

 mass filled with transparent crystalline carbonate of lime, while 

 the former vesicular interlaminar interstices were replenished 

 with turbid, milky dolomite. Sections through such specimens 

 in vertical direction, show the transparent casts of the tissue 

 pillars as tubular channels, and in horizontal sections the same 

 appear to be circular orifices surrounded by a massive interstitial 

 wall substance. 



Silicified specimens occasionally occur in which the interlaminar 

 spaces filled with silica are the only part preserved, while the 

 actual skeleton has been removed by solvents, and the space once 

 occupied by it remaining hollow, we then see the mass intersected 

 b3^ innumerable small circular channels. 



I had the good fortune to find in the drift of Ann Arbor some 

 calcareous specimens in which the original tissue mass is pre- 

 served, represented by a non-transparent, dull, calcareous matter, 

 while the cellulose interlaminar interstices are replenished with 

 clear, transparent carbonate of lime. 



They consist of a succession of thick, concentrically superim- 

 posed, undulating and monticulose layers from two to six milli- 

 meters in thickness, which are generally demarkated from 

 one another by darker colored division lines of greater density 

 than the remainder of the lamina. Each such larger lamina 

 represents a certain uninterrupted period of growth during 



