﻿100 PROF. E. W. SKEATS ON THE [Feb. I905, 



(1) In those coral-islands which are remote from laud-areas and 



volcanic rocks, the amount of insoluble residue in the lime- 

 stones was negligible. 



(2) In coral-islands associated with volcanic rocks many of the 



limestones were found to be practically devoid of residue, 

 but those in the proximity of the volcanic masses contained 

 a larger quantity, amounting in some cases to over 4 per 

 cent. 



It will be noticed that in a recent coral-reef, either the whole 

 or some part of the materials of which it is composed is devoid of 

 insoluble residue. It is obvious that this total or partial absence of 

 insoluble residue ought to hold good as well for a fossil coral-reef 

 as for a recent one. I determined, therefore, to visit the Dolomites 

 of the Tyrol, to make representative collections in this much- 

 debated region, and to see whether a chemical and microscopical 

 examination of the specimens would afford any evidence as to the 

 mode of origin of the deposits. By the favour of the Council of 

 this Society in making me the first recipient of the proceeds of the 

 Daniel-Pidgeon Fund, I was enabled to spend a considerable part 

 of the summer-vacation of 1903 in making typical collections of the 

 Triassic rocks in the district. I am indebted to Prof. Judd for 

 giving me the opportunity of analysing the material collected, and 

 I am glad to be able to lay before the Society the results of the 

 investigation. 



The area visited is all included within the roughly- circular basin 

 in which the typical dolomites of Southern Tyrol are best seen. The 

 fundamental rocks, exposed only at the border of the area, consist 

 of quartz-phyllites and schists of great antiquity, possibly of 

 Archaean age. The earliest sediments are Permian, and succeeding 

 these are the Triassic deposits, which cover the greater part of 

 the basin. The Alpine movements of the mid- Tertiary age 

 originated a series of flexures and faults, of which the majority 

 trend roughly north-and-south and east-and-west. The shallow 

 anticlines formed as a result of these movements have, to some 

 extent, determined the directions of the valleys. The northern and 

 southern valleys include those of the Eisack, Fassa, Agordo, and 

 Ampezzo. The eastern and western valleys are not so well defined 

 (with the exception of the Pusterthal in the north of the area), and 

 for the most part form subsidiary depressions joining the more 

 prominent northern and southern valleys. Over the greater part of 

 the area, the dolomite-rocks of the Upper Trias are exposed at the 

 surface, while the Middle and Lower Triassic deposits are only 

 seen on the flanks of the valleys. The Permian rocks are occa- 

 sionally exposed in the deepest parts of these valleys. The strati- 

 graphical succession varies somewhat in different areas, owing to 

 the heteropic character of the deposits. In three typical localities 

 it is as follows : — 



