﻿Vol. 6 I .j DOLOMITES OF SOUTHERN TYROL. 141 



the pressure was consequently lowest, yielded the smallest per- 

 centage of dolomite. 



Dr. C. G. Cullis said that it was very satisfactory to find that 

 the Author's investigations had led him to conclusions which were, 

 in the main, harmonious with those already arrived at, along other 

 lines of evidence, by such eminent geologists as Baron F. von 

 liichthofen and Dr. E. von Mojsisovics, namely, that these great 

 limestone-masses of Southern Tyrol represent the denuded remains 

 of Triassic atolls and coral-reefs, and that the peculiar lithological 

 characters of the rocks, as well as the distinctive physical features 

 of the region, were merely expressions of this fact. The Author 

 had been led to this conclusion by observing the great similarity 

 which the rocks presented, in their chemical composition and 

 detailed microscopic characters, to those which enter into the con- 

 stitution of recent coral-reefs. From what he himself had seen of 

 the microscopic character of coral-reef rocks, as exemplified by the 

 cores of the Funafuti boring, he was glad to be able to confirm this 

 resemblance, which in many cases is so striking as to make it almost 

 impossible to avoid the conclusion that, notwithstanding their great 

 difference in age, the two sets of rocks must have come into 

 existence under substantially the same conditions. 



Eeferring to the explanation of dolomitization, in terms of the 

 relative solubility of calcium- and magnesium-carbonates under 

 varying pressures, which the Author had suggested, he hoped that 

 this would secure the favour and support of chemists. Speaking 

 from recollection, he could not recall any fact or phenomenon 

 presented by the dolomitization of the Funafuti rocks which did 

 not find a satisfactory interpretation in the light of this simple 

 but ingenious explanation. It seemed to him to provide the 

 key to a problem which had puzzled geologists since the days 

 of Leopold von Buch. 



Mr. Dixon referred to the evidence that some dolomite in the 

 Carboniferous Limestone of Pembrokeshire and Caermarthenshire is 

 associated with shallow-water conditions. 



Prof. Watts drew attention to the probably shallow-water 

 dolomites near Charnwood Forest, and to the base of the Car- 

 boniferous Limestone in Ireland, frequently either a dolomite, or a 

 conglomerate or grit cemented by dolomite. He further pointed 

 out that, although the Author had made an extremely-important 

 comparison between the dolomites of Southern Tyrol and coral- 

 limestones, and had shown that both of them lacked insoluble residue 

 (which was a common ingredient in calcareous deposits), the com- 

 parison could not be followed to its logical conclusion until other 

 calcareous sediments, such as those of the Gulf of Mexico and the 

 Gulf-Stream areas, had been thoroughly examined. 



The Author thanked the previous speakers and the Fellows 

 present for their generous reception of his paper, and, in reply to 

 Dr. Armstrong, stated that microscopical examination of lime- 

 stones containing 10 or 12 per cent, of magnesium-carbonate failed 

 to show the presence of magnesite as recognizable crystals. 



