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these ancient actuaries Mill be found in the third volume ofthe Geological Transactions.

The tract around Bovey Tracey in Devon , which exhibitsseveral beds of wood-coal, alternating with the alluvial debrisof granitic rocks, is another instance of such an aestuary.

The formation of peat bogs is another of the geologicalchanges in actual progress. Dr. Mac Culloch in a most ablepaper published in the Edinburgh Philosophical Journal for1820, has treated this subject in the most precise and satisfac-tory manner : he considers peat bogs as divisible (from theconsideration of the vegetables which compose them, and thecauses which concur in their formation) into the followingvarieties ; mountain, marsh, forest, lake, and marine peat: inthe progress of the work we shall have occasion to explainmore fully, and to apply his principles. The formation of peatbogs often occasion, or at least materially contribute to, thepartial filling up of lakes, the extension of marsh lands alongthe coast, Jcc. Much valuable information concerning theseprocesses may be found in De Luc’s Travels in the north ofEurope .

The materials accumulated in alluvial districts are usually ina loose form, as sand, marie, and clay. The formation of com-pact rocky masses is of more rare occurrence ; under favorablecircumstances, however, and especially along the coast, sand-stones are formed from the consolidation of the drift sand, andwhere the oxide of iron is present to act as a cement, the pro-cess goes on rapidly : the northern coast of Cornwall affordsextensive examples of this process (see vol. 1 of the CornishGeological Transactions). Captain Beaufort describes a line ofpetrified beach as extending along various points of the coast ofCaramania ; the same thing is common in the Bahama Isands,and the human skeleton brought from the beach at Guada-loupe, and preserved in the Biitish Museum, was imbedded ina mass of this description* : it is unnecessary to add that ma-rine remains are commonly dispersed through rocks of thisdescription ; occasionally comminuted shells form almost theentire mass, in which case the rock is of course calcareous : anear resemblance to some of the oolites may also be observed inthese recent formations. Calcareous rocks are often also de-posited from the waters of existing rivers or lakes in largemasses. The celebrated Travertino of Rome is thus formed,and Germany affords some similar instances. The deposits ofpetrifying waters, such as the Baths of San Filippo, the stalac-

* “ The occurrence of the Bulimus trifasciatus, a very common WestIndian shell, in this mass, strongly indicates its modern formation.”

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