Prof. Garwood — Calcareous Alga}. 551 



Torinosu Limestone, Japan. This discovery is of interest, as it carries 

 the known occurrence of Solenopora up to the base of the Cretaceous, 

 in which formation Lithothamnion appears and thenceforward becomes 

 the chief representative of the rock-building Coralline Algae. 



Cretaceous. 



We here reach the period when Lithothamnion and its allies begin 

 to make their appearance. They have not yet been recognized in 

 British rocks, but are widely distributed in deposits on the Continent. 

 They occur in the Cenomanian of France, in the Sarthe and the Var, 

 but especially in the Dauian of Petersburg, near Maestricht. 



Other forms which maj'' be mentioned are Diplopora and Triplo- 

 porella. The former is met with abundantly in the Lower Schratten- 

 kalk in certain districts, especially Wildkirchli, where it plays 

 a considerable part in the formation of the deposit.^ 



Tertiaky. 

 In Britain no example of marine Calcareous Algse have, so far as 

 I am aware, yet been reported, but considerable deposits of freshwater 

 limestone, rich in remains of Ghara^ have for long been known from 

 the Oligocene of the Isle of Wight. 



Foreign Tertiary. 

 On the Continent, however, thick deposits rich in Lithothamnion 

 and Lithophyllum have been known for many years. Of these I may 

 mention especially the well-known Leithakalk of the Vienna Basin 

 and Moravia. It will be remembered that it was these deposits which 

 formed the subject of Unger's important monograph in 1858.' 



Conclusions. 

 The facts given above regarding the geological distribution and 

 mode of occurrence of these organisms lead us to several interesting 

 conclusions. In the first place there can be no doubt from the 

 examples described above that they play a very striking part as I'ock- 

 builders at many different horizons in the geological series. At the 

 same time it is evident that not only are certain forms restricted to 

 definite geological periods but also that they had a wide geographical 

 range, and on this account these organisms will often be found 

 valuable as zonal indices either alone or in conjunction with various 

 other organisms. As an example of this wide distribution we may 

 cite Solenopora compacta, which flourished so abundantly during 

 Llandeilo-Caradoc times not only in the Baltic area and Scotland 

 but also in England, Wales, and Canada; again, the wonderfully 

 persistent development of the Rhabdnporella facies over the whole of 

 the Baltic area at the close of Ordovician times was of so marked 

 a character that even boulders of these rocks scattered over the 

 IS'orth Grerman plain can be made use of in tracing the direction of 

 flow of the ice-sheet during Glacial times. 



^ Arbenz. Vierteljahrsschr. Naturf. Ges. Zurich, vol. liii, pp. 387-92, 1908. 

 ^ This form, though till lately included among the green algse, is now usually 

 placed in a distinct group — the Charophyta. 



' Denksch. k. Akad. Wiss. Miinchen, vol. xiv, p. 13, 1858. , 



