200 Report of the State Geologist. 



and lastly the presence of a very pure sea water, that is to 

 say, not mixed with fresh water and free from mud. It is 

 proved that whatever may be the differences of the groups to 

 which these animals belong, these conditions remain the same 

 through all the different geologic epochs The calcareous masses 

 where coral structures are found are always very pure and 

 saccharoidal in texture, and the interstices of the polyps show no 

 trace of marl or clay/ The same conditions are requisite for the 

 existence of numerous forms belonging to all the classes of the 

 animal kingdom which live on the corals and appear and 

 disappear together with 'them. 



The coral formations of the Upper Jurassic are found mostly 

 within the circumference of the Paris basin, in the Jura, in Switzer- 

 land and in Suabia. Wherever those deposits are not represented, 

 there exist deposits of marl or clay rich in Ammonites or 

 Lamellibranchs. The earlier school of geologists admitted that 

 all the deposits of coral origin were contemporary, and united 

 them under the name of terrain cor allien'^ the formations of other 

 origin were referred either to an anterior epoca (Upper 

 Oxfordian) or to a more recent epoch (infra Cretaceous). The 

 works of Op pel, Mosch, and more especially of the Abbe Bour- 

 geai^ have demonstrated that these reefs were formed at various 

 epochs, and that for every different coral facies are always found 

 corresponding muddy facies and pelagic facies, of the same age^ 

 but very different in the character of th- fossils. 



The reef of Yalfin, which dates from the Pterocerian epoch, 

 may be taken as the type of these formations. It extends for 

 about 80 kilometres ; its form is very irregular in every sense ; 

 on one vertical line are found lateral expansions which rest on 

 successive deposits, like caps and columns. The mass of the 

 reef is a limestone of corallic' origin; here and there in the 

 irregular mazes is found the especial fauna rf the reefs, 

 which is here very abundant. The polyps embrace no less 

 than 62 species ; toward the center arborescent forms predomi- 

 nate, sometimes over one metre m height, such as Aplosmilia, 

 Stylosmilia^ Calamophyllia^ etc. Massive asteriate forms are also 

 found, as Tkamnastrcea^ m^andrinoid forms {Pachygyra, Den- 

 drogyra). Lastly the simple polyps, represented by Montlivaultia, 

 are especially alDundant in the rocks with the rest of the fauna. 

 This fauna is particularly rich in forms having a thick test^ 

 which is in accordance with the fact that the corals, grow- 

 ing in regions beaten by the waves, must necessarily be pro- 

 vided with a strong power of resistance. Small sized species 

 having a thinner covering are only found in well sheltered places. 



* E. Bourgeat, Recherches sur les formations coralligenes du Jura meridional, 1887. 



