Structure of the Austrian Alps, fyc. 109 



2. He states that the tertiary formation of Hairing is en-> 

 tirely of freshwater origin. We prove that it contains several 

 species of marine shells ; from which we conclude (contrary 

 to the opinion of Dr. Boue, but on evidence we think not short 

 of demonstration,) — that the marine tertiary deposits of the 

 Alps do sometimes ascend far up the transverse secondary 

 valleys. 



3. He contends that the tertiary formations on the flanks of 

 the Austrian Alps commence with the superior divisions of that 

 class of rocks, the lower divisions being entirely wanting. We, 

 on the contrary, have shown, both by transverse sections and 

 suites of fossils, that some of the inferior groups of the tertiary 

 deposits in the Gratz basin are of the age of the London clay. 

 So far there is a difference between Dr. Boue and ourselves 

 on what we consider questions of fact. 



4. We also differ from him considerably on questions of opi- 

 nion. For example : he describes great masses of calcareous 

 conglomerate in the Salzburg Alps, which he compares with a 

 part of the nagelfliih of Switzerland, and places in the secondary 

 system under the green-sand. We have not examined the 

 nagelfliih, and can therefore offer no opinion respecting its age ; 

 but of late years it has been generally considered tertiary. In 

 the Salzburg Alps, the great masses of calcareous conglome- 

 rate are chiefly found on the outskirts of the chain, and form 

 the base of a new series of deposits which are physically and 

 zoologically separated from the older system; and are, if we mis- 

 take not, newer than the chalk. Occasionally, as in the valley 

 of Gosau, they appear far within the chain : but in that case 

 they are unconformable to the rocks which surround them ; 

 and there is then no means of determining their age, except 

 by the help of their fossils, or by comparing them with the cor- 

 responding beds on the outskirts of the chain. After making- 

 use of both these means of comparison, we concluded that the 

 overlying conglomerates of Gosau were newer than the chalk : 

 and in our examination of other parts of the eastern Alps we 

 did not find any large masses of coarse, calcareous conglome- 

 rate subordinate to the newer secondary system. 



5. M. Boue seems to attribute much greater importance, 

 than we do, to mere mineralogical distinctions. We know 

 numberless instances in which green-sand above the chalk 

 cannot be distinguished from green-sand below the chalk. 

 Some of the lacustrine formations of central France have been 

 mistaken for old secondary deposits. We have found, on the 

 outskirts of the eastern Alps, fossils of the London clay alter- 

 nating with rocks resembling our coal grits, and masses of con- 

 glomerate like those subordinate to the oldest secondary rocks ; 



and 



