20 SCIENCE PROGRESS. 



which may frequently result in the removal of all signs of 

 phytogenetic origin. On the other hand, in many calcareous 

 beds the percolating waters have not found the same 

 amount of carbonic acid, and their solvent power has not 

 been sufficient to effect the destruction of the organic 

 remains from which the strata have been formed. If the 

 calcareous deposits are protected from the circulation of 

 carbonated water by overlying impervious beds, the organic 

 structures would not be removed. It would seem, therefore, 

 that under certain circumstances, in which calcareous depo- 

 sits are freely exposed to infiltrating water, there is a much 

 greater probability of all structure being removed in the 

 case of those formed from calcareous algae than in deposits 

 which are not of phytogenetic origin. Walther's researches 

 are of extreme importance from a geological point of 

 view ; they at least show that the study of living calcareous 

 algae may possibly lead the petrologist to approach from a 

 new standpoint the difficult question of the genesis of 

 structureless limestones. 



In two recent numbers of the Geological Magazine 

 Brown 1 has given some account of another calcareous or- 

 ganism, Solenopora, which his investigations compel us to 

 annex as a member of the Floridece. It has a wide geo- 

 graphical distribution, and its geological range extends 

 from Ordovician to Jurassic times. The author describes 

 several species from various districts and horizons, and con- 

 cludes his remarks with a discussion of the botanical posi- 

 tion of the genus. He compares it with Lithothamnion, 

 Corallina, and other calcareous genera: "the form of the 

 cells and cell walls, the method of increase, and the arrange- 

 ment of the tissue cells in the various species of Solenopora 

 bear strong evidence of relationship between that genus and 

 the calcareous algae ". Additional evidence of taxonomic 

 value is derived from the occurrence of reproductive organs 

 in some few specimens. There can be little doubt that 

 Solenopora should be included among the rapidly growing 

 list of fossil calcareous algae which must claim the atten- 



1 Brown, p. 200, pi. v. 



