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In Madeira and the Canary Islands streams of lava of subaerial origin are often divided by red bands of laterite, probably ancient soils formed by the decomposition of the surfaces of lava-currents, many of these soils having been coloured red in the atmosphere by oxide of iron, others burnt into a red brick by the overflowing of heated lavas.
I saw nothing beyond a succession of ridge-backs and shrinkage-crevasses, disposed upon an acute angle. These ragged, angular, and mostly cuboidal blocks, resembling the ice-pack of St. Lawrence River, have apparently been borne down by subsequent lava-currents, which, however, lacked impetus to reach the lower levels of Las Canadas.
The depth of overlying peat affords no safe criterion for calculating the age of the cabin or village, for I have shown in the "Principles of Geology" that both in England and Ireland, within historical times, bogs have burst and sent forth great volumes of black mud, which has been known to creep over the country at a slow pace, flowing somewhat at the rate of ordinary lava-currents, and sometimes overwhelming woods and cottages, and leaving a deposit upon them of bog-earth 15 feet thick.
Lava-currents have also flowed upon the land and along the bottom of the sea volcanic sand, pumice, and scoriae have been showered down so abundantly that whole cities were buried- tracts of the sea have been filled up or converted into shoals and tufaceous sediment has been transported by rivers and land-floods to the sea.
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