﻿l^t) FKOF. E. W. SKUATS ON THE [Feb. I905, 



Mendola Dolomite. 



Examination of a single specimen failed to show any trace of 

 organisms. 



Lower Muschelkalk. 

 Lamellibranchs were noticed in the only section examined. 



Deposits above the Schlern Dolomite. 

 Dachstein Dolomite. 



Two sections were examined, and it was found that one slide 

 contained remains of what were probably lamellibranch-shells, while 

 both sections showed meandrine structures which were possibly tho 

 remains of corals. 



Raibl Beds. 



Pour sections were cut ; of these, one showed the transverse 

 section of a compound coral, while the other three were apparently 

 devoid of organisms. 



YI. Belations between the Fossils and the Origin 

 oe the Rocks containing them. 



Before attempting to interpret the results arising from the 

 examination of the fossil contents of these rocks, especially of 

 the Schlern Dolomite, it will be convenient to consider briefly 

 our present knowledge as to the organisms composing coral- 

 limestones, and the changes that they undergo. 



In the first place, it has been shown that corals play a much 

 less important part in building up coral-reefs than was formerly 

 supposed. 1 Calcareous algae are often more abundant than the 

 corals ; foraminifera and echinodermata often bulk largely ; and 

 polyzoa, lamellibranchiata, and other organisms are occasionally 

 present in fair abundance. 



The sequence of mineralogical and structural changes which coral- 

 limestones undergo — a subject originally studied by Dr. Sorby — has 

 in recent years been rather closely investigated. I have already 

 dealt with some of the more striking changes occurring in upraised 

 coral-islands 2 ; while Dr. C. G. Cullis 3 has examined in greater 

 detail the mineralogical constitution and structural changes in thin 

 sections of the rocks from the Funafuti boring. 



It is found that organisms, the skeletons of which are composed of 

 aragonite, are abundant in the most recent limestones, but gradually 

 become recrystallized as calcite ; and this change is accompanied by 

 a loss of structure in the organism. For this reason, all the reef- 

 forming corals, the gasteropoda, and some of the calcareous alga?, 



1 R. L. Sherlock, Bull. Mus. Comp. Zool. vol. xxxviii (1903) p. 349 ; E. W. 

 Skeats, ibid. vol. xlii (1903) p. 53 ; & G. J. Hinde, ' Funafuti Report ' Roy. Soc. 

 (1904) p. 332. 



2 Bull. Mus. Comp. Zool. vol. xlii (1903) p. 53. 



3 ' Funafuti Report ' Roy. Soc. (1904) p. 392. 



