40 The Dolomite Mountains. 
crossing the mountain summits, and adds greatly to the sublimity of 
their aspect. There are no fossiliferous equivalents in England of the 
deposits of St. Cassian and Hallstadt. Our White Lias is supposed 
to represent some higher beds, which have been called ‘ Rheetic,’ 
after the Alps that divide Carinthia from the valley of the Inn. 
In the last pages of this substantial volume we come to their most 
important geological topic, the origin of the Dolomites. Von Buch 
asserted, and most geologists have since believed, that they originally 
consisted of carbonate of lime, and he attributed their conversion to 
the influence of magnesian vapour evolved from the augitic porphyries 
beneath, during a period of depression. Unfortunately, it is no easy 
matter to vaporize magnesia; and, although it is highly probable 
that water has done more to metamorphose rocks than even the 
Plutonic fires, yet it is difficult to accept theories requiring that the 
sea should remain for ages at the boiling point. Mr. Sterry Hunt 
has made some observations on the action of solutions of bicarbonate 
of soda upon sea-water, by which hydrated carbonate of magnesia 
might be produced, and afterwards converted, with the aid of heat 
and pressure, into Dolomite. Sir R. Murchison and Prof. Harkness 
have still more recently suggested that the frequent association of 
gypsum with Dolomite supports the notion that the magnesia origi- 
nally existed a3 a sulphate (Geol. Journ. May 1864). Some portions 
of the English magnesian limestones may have been originally de- 
posited in the form of sediment derived from the waste of Dolomite 
mountains ; but. the concretionary beds, and the magnesian carboni- 
ferous limestone of Breedon, are probably metamorphic. The ques- 
tion is one for the chemist, and all the geologist can do is to set. the 
facts rightly before his fellow-worker. 
The peculiar form of the Dolomite mountains presents another 
question, admitting of a more satisfactory solution. Dr. Richthofen 
has called attention to their remarkable resemblance to coral-reefs, 
such as we know them to be from soundings, and theoretical considera- 
tions. The wood-cut (for the use of which we are indebted to the 
publishers) will give an idea of the outline of a group of Dolomite 
mountains, but a more vivid impression is conveyed by Mr. Churchill’s 
comparison of them—scattered over the porphyritic platforms—to 
icebergs stranded ; so little connection did they appear to have with 
the associated rocks. Sir R. Murchison observed traces of bedding on 
some of their precipices, seen in a favourable light ; but they usually 
appear devoid of stratification, and are deeply divided by vertical 
fissures. There is an unromantic view of the Dolomitic Podoigebirge, 
forming the frontispiece to Dr. Klipstein’s work on the fossils of St. 
Cassian,* which even more strongly than Mr. Gilbert’s views brought 
to mind a rude outline of a Red Sea coral-reef made by the engineer 
who erected the lighthouse on the Uschruffee Islands. On cutting 
down the reef, he found that the coral was not solid, but formed 
of irregular columns, which expanded their summits laterally as they 
reached the limit of growth at the low-water line, leaving fissures and 
* The collection made by Dr. Klipstein is in the British Museum. 
