810 Professor Jameson cm Rocks formed by Hot Springs^ 
ii 
stallise, and assume their various permanent characters. The 
amygdaloidal traps appear to be formed in those cases where car- 
bonate of lime is present ; the obsidian where dissolved silica pre- 
vails ; and in the same general way we might account for the for- 
mation of the other rocks. In the collection of Islandic Mine- 
rals presented to the Museum of our University by Sir George 
Mackenzie, there are specimens of a few of these thermal 
rocks ; but the series not being complete, we cannot from it 
draw up an accurate statement of the characters which they 
exhibit in hand specimens, far less point out in a satisfactory 
manner, those general features that characterise them as a mem- 
ber in the grand series of mountain rocks. Menge has promis- 
ed to transmit a set of these remarkable rocks, which will afford 
us an opportunity, in some future number of our Journal, to 
make our readers more particularly acquainted with them. 
In other parts of the world, where hot-springs have flowed, 
or still continue in activity, similar formations, we have no 
doubt, will be met with. The breccias and tuffas in the tra- 
chyte district in Hungary, and which contain opal and opalised 
wood, appear to be formations of hot-springs. Probably even 
some of the trachytes have been formed in a similar way. The 
same remark applies to some rocks found in Auvergne. But 
besides these trap and porphyry rocks, hot-springs also throw 
out and form rocks of a calcareous nature. The hot-springs of 
Carlsbad in Bohemia are of this description, and the well known 
hot-springs of San Filippo in Tuscany, have formed a hill of 
calcareous tuffa, in many places as compact and hard as lime- 
stone The famous rock named travertino by the Italians, 
and which abounds in South-western Italy, is a product partly 
of hot, partly of cold springs. The ancient temples, and the 
gorgeous palaces and churches of Borne, and indeed the whole 
of the streets and squares of the former Mistress of the World, 
are built of concretionary masses which have been deposited by 
springs. 
There are many considerable hot-springs around Guancaveli- 
ca in South America, the waters of which spread over the 
neighbouring country, and deposit upon it an ash-grey or whit- 
* In our present number, we have inserted an interesting account of the 
spring of St Filippo, by our acute and learned friend Dr Gosse of Geneva. 
