The Pleistocene strata–the latest of the geologists' list–are the river gravels of existing river valleys, the deposits in many caves, and the sands and clays piled up by ice action during the repeated glacial extensions or epochs of glaciation which alternated with milder climate for many thousands of years over north and middle Europe. It is identical with the Palæolithic period, which, however, probably extends beyond it into the Pliocene and even further back. In the later deposits of the Pleistocene, which necessarily have been less frequently disturbed and re-deposited than the older ones, we find more numerous remains of man's handwork, and in less disturbed order of succession, than in the older deposits. Lately we have obtained in East Anglia beautifully-worked flint implements–the rostro-carinate, or eagle's beaks–from below shelly marine deposits–the Red Crag of Suffolk and the Norwich Crag–the oldest beds of the Pleistocene. They were made by men who _lived_ in the Pliocene period, and carry the ancient Stone period of man back to a much earlier period than was admitted nine years ago. The Pleistocene series or "system" of strata–also called the "Quaternary" to mark its distinction from the underlying long series of "Tertiary" strata–does not comprise the actual surface-deposits in which the remains of Neolithic man are found. It is usual, though perhaps not altogether logical, to separate these as "Recent" and to begin the long enumeration of "geologic" strata after a certain interval when the relative levels of land and sea and the depth of river-valleys were not precisely what they are to-day, and the human inhabitants of Western Europe were hunters using rough unpolished flint implements–in fact, when the "Palæolithic" period of human culture had not given place to the "Neolithic," which was after some ten thousand years itself to be superseded by the age of metals. "Prehistorians," the students of prehistoric man–divide the Pleistocene series of deposits with a view to a systematic conception of the successive changes of man and his surroundings during the period occupied by their deposition, into an upper, a middle and a lower group–and further have distinguished certain successive "horizons" in these groups–characterized by the remains of man and animals which they contain. They are exhibited in the tabular statement here given in the ascertained order of their succession, and are represented in the southern part of Britain as well as in France. HORIZONS OR EPOCHS OF THE PLEISTOCENE OR QUATERNARY SYSTEM _A._ UPPER PLEISTOCENE (post-glacial; also called epoch of the Reindeer).