But man's influence on the landscape has not consisted wholly in removing what he found to be obnoxious. He has introduced many forms of vegetation among those indigenous to the country. He has thus converted thousands of square miles of scrub, moor and woodland into gardens, parks, meadows and corn-fields. He has replaced some parts of the primeval forest by plantations of a different type, wherein the native hardwood trees are mingled now with larch, silver-fir and other trees which seem to have had no place in the original flora. But the minor modifications of the landscape within historic time have not been merely those due to human interference. Nature has been ceaselessly at work in slowly, and for the most part imperceptibly, changing the forms of the ground. The streams have dug their channels deeper into the flanks of the hills and have spread their alluvial soil further and wider over the valleys and lake-floors. The frosts of winter have been splintering the crags, the springs have been sapping the cliffs, and from time to time landslips have been launched into the stream-channels below. The sea has cut away large slices of land from some parts of the coast-line, while to others it has added strips of alluvial ground and mounds of shingle. We have seen too that underground movements have contributed to modify the landscape in some parts of the country, certain tracts having been upraised so as to expose broad spaces of flat ground, while others have been submerged beneath the sea which now ascends into what were formerly open valleys. This sinking of the land in southern England, inasmuch as it helped to separate Britain from the continent, must be regarded as probably the most far-reaching change that has affected the landscape of this country since the days of Neolithic man. FOOTNOTES: [1] The substance of this Essay formed an address to the Oxford University Scientific Club, in 1887. [2] This illustration of the subject is discussed in my _Geological Essays at Home and Abroad_, p. 253. [3] This part of the subject is more fully treated in the two following essays. [4] A portion of this passage has been inserted in my _Scenery of Scotland_. [5] This plain is one of the upraised marine platforms referred to in a later part of this Essay. [6] Dr. Joyce's excellent _Irish Names of Places_ is the best authority on this subject. II Landscape and the Imagination[7]