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476 careful researches of modern times have, however, in most cases, removed all sources of error under this head; and the fact of this co-existence being now established, we are to a great extent able to eliminate the doubtful portions of the older-recorded observations, and to give to the residue a value which it did not formerly possess.

Before proceeding, however, to discuss any of the evidence afforded by cavern-deposits on the existence of man and the nature of his tools and implements in those early days, it will be well to say a few words both as to the nature of ossiferous caves in general, and as to the probable manner in which their contents were deposited in the positions in which we now find them. In doing this, I shall be as brief as possible, and will content myself with referring the reader, who is desirous of further details, to works more strictly geological.

What must strike all observers at the outset is, that caverns vary greatly both in their character and in their dimensions; some being long and sinuous, in places contracting into narrow pas- sages, and then again expanding into halls more or less vast; while others are merely vaulted recesses in the face of a rock, or even long grooves running along the face of some almost perpendicular though inland cliff. Most of the English ossiferous caverns belong to the former class, while the majority of those of the Dordogne and some other parts of the south of France belong to the latter. These recesses and rock-shelters apparently owe their existence to a somewhat different cause from that which produced the long sinuous cavities. They usually occur in cliffs of which the stratification is approximately horizontal, but where the different beds vary much in their degree of hardness and permeability to water. The softer strata, underlying the harder masses, are in consequence more liable to be acted upon by rain, wind, and frost, so that they weather away faster, and leave deep recesses in the face of the cliffs, admirably adapted for conversion, with but little trouble, into dry and commodious shelters from the weather, which have in consequence been seized on for habitation by man from the earliest times to the present day. Caves of this character may possibly in some rare instances have been due to the eroding action of the sea, before the land was elevated to its present