650 E. Blackwelder — Reef of Calcareous Algce (?.). 



The minute cellular texture that maj have been possessed by 

 the organisms could not be expected to survive the crystalliza- 

 tion which inevitably affects lime-carbonate masses with the 

 march of time. 



Since corals and bryozoans are often found well preserved in 

 rocks no more altered than these, their absence here creates a 

 strong presumption that the domes are hot of coralline or bryo- 

 zoan origin. They are best referred to some organism of 

 extremely delicate internal structure such as many of the 

 modern calcareous algae. In view of the fact that algae even 

 to-day are known to construct large and stony masses of lime 

 carbonate which constitute important or even predominant 

 parts of many so-called coral reefs, the writer believes that the 

 bee-hive shaped masses here described were built by colonies 

 of algae. The internal structure suggests that during the 

 growth of a given colony, it was first enlarged by the addition 

 of concentric crusts, but that after reaching a diameter of two 

 to three feet, a process of budding set in all over the periphery, 

 and thereby produced a multitude of miniature colonies which 

 are now represented by the mammillary outer layer. The life 

 of the reef may well have been terminated by the increasing 

 muddiness of the water under the influence of some physio- 

 graphic change that ensued. 



Madison, Wis., Feb. 8, 1915. 



