Page:Memoirs of the Geological Survey of Great Britain, Volume 1.djvu/411

398 analogy with the latest zoological conditioiis of the west of Europe, including Britain, during the epoch preceding that by common consent of geologists termed historical.

Connected with the latest changes included in the historical period are the phenomena of raised beaches, properly so called, distinguished by Mr. Smith from the true glacial beds and containing numerous testacea all characteristic species and similarly associated with those now living in the British Seas; and the raised estuary and beach-beds described by Sir Henry De la Beche in the Report on the Geology of Devon and Cornwall. In that work there is described a most interesting section observed by Mr. Henwood at the Carnon Stream Works, where we find sand with sea shells covering the remains of a forest, containing bones of the red deer and human skulls, which rests in turn on tin ground considered by Sir Henry as equivalent to the rhinoceros gravels of Lyme Regis. On the subject of the evidences of the latest changes of level on our southern coasts the essays of Mr. Austen in the Geological Transactions are full of valuable observations.

The agency of man has both added to and diminished the number of our plants and animals. The epochs of the destruction of the wolf and of the beaver are historical events, whilst other more useful creatures have been introduced and naturalized. Even among the invertebrata we find man involuntarily adding to and diminishing the number of our resident species. Now, the draining of lakes destroys the rarer freshwater mollusks, whilst the formation of canals diffuses new forms—as in the case of Dreissena polymorpha—all over the country. The progress of cultivation drives before it, and finally banishes, many an indigenous but useful flower, and at the same time introduces others as useless, and perhaps not so harmless, to take its place. With the good comes the evil, and the hand that sows the corn diffuses the dodder. Fortunately the records of natural history have been begun in good time, and the influence of man's agency through the progress of civilization, and. its accompaniments, is of too recent action to affect the statistics of our science.

Great as the changes appear to be affecting the disposition of land and water, during recent geological periods, as compared with the present, assumed by me in this essay, I cannot but express my conviction that future research will not only confirm these, but prove that still greater took place during the epochs under inquiry. The phenomena of the glacial formations, the peculiarities in the distribution of the animals of that epoch, and in the relations of the existing fauna and flora of Greenland, Iceland, and northern Europe are such as strongly to impress upon