﻿Vol. 6 1.] 



DOLOMITES OF SOUTHEKN TYKOL. 



101 



Sehlern Area, 

 North Side. 



Seiser Alp. 



Tre Croci and Cortina. 



Dachstein Dolomite. 

 Raibl Beds. 





Dacbstein Dolomite. 

 Raibl Beds. 







Pachycardium-Tuffs . 



Sehlern or St. Cassian 

 Dolomite. 



Sehlern Dolomite. 



St. Cassian Marls. 



St. Cassian Marls and 

 Limestones. 





Upper Wengen Beds. 



Wengen Sandstones. 



Augite-Porphyrite 



Augite-Porphyrite 



Wengen volcanic rocks. 



(Lower Wengen). 



(Lower Wengen). 





Buchenstein Limestone. 



Buchenstein Limestone. 





Mendola Dolomite. 



Mendola Dolomite. 





Dont Scbiefer 



Dont Schiefer. 





(Lower Muschelkalk). 







Campiler Scbiefer. \ 

 Seiser Scbiefer. j 



Werfen Beds. 





Permian. 







The dolomite seen on the north-eastern flank of the Sehlern 

 Mountain, and in the Marmolata, Langkofl, 1 and Plattkofl massifs 

 corresponds in age both to the Wengen and to the St. Cassian Beds. 

 When followed eastward and northward, the dolomite is seen to 

 rest upon St. Cassian deposits, and represents only the upper part 

 of the dolomite from the areas just mentioned. 



The Sehlern Dolomite is the massive deposit that gives the 

 characteristic appearance to many of the isolated massifs. It is 

 this deposit which is generally claimed as being of coral-reef origin, 

 and it is this horizon which I have particularly examined. The 

 Mendola Dolomite has also been supposed to owe its origin to coral- 

 reef conditions in mid-Triassic times. 



II. The Chemical Evidence. 



The results of the chemical analyses of the specimens obtained 

 from the localities visited will now be given. A few complete 

 gravimetric analyses were made, and the results of these are 

 recorded to two places of decimals. In the case of the majority of 

 the specimens, only the insoluble residue and the iron and alumina, 

 when present, were gravimetrically determined ; the calcium was 

 estimated volumetrically by a method described fully in a previous 

 paper, 2 and the amount of magnesium was obtained by difference. 

 The results of the volumetric analyses are recorded only to one 



1 The section of the rocks on the north-western flank of the mountain shows 

 that the massive dolomite is underlain by bedded dolomitic limestones closely 

 resembling the Buchenstein Limestone. Mrs. Ogilvie Gordon, however, has 

 proved St. Cassian Beds on the eastern flanks of the mountain, and believes that 

 the dolomite-masses overlie the St. Cassian Beds. 



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



