For some years past it has been a commonly received doctrine among continental geologists that lava-streams could not consolidate on slopes or declivities of more than five degrees. When, then, solid lavas were found in various volcanic mountains at high angles, other sources of origin than the mere outflow from their respective craters had to be sought; and thus arose the theoretical idea of the formation of the cone or crater at a late period of the volcano's existence—after for ages numerous lava-streams had issued from it and had become consolidated one over the other into stony beds on successive flat plains—by the uprise and bursting of a vast dome or bubble; and such was called a “crater of elevation”.