North Germany. The scientific value of the contents of inhabited caves may be paralleled with that of the drift deposits, only greater care has to be taken in dealing with the former, as their deposits are subject to disturbances by later visitors, whether man or beast. There is one physical feature peculiar to caverns which deserves a passing word, as it is claimed to have a special chronological value, and that is, the deposition of stalagmite. If a layer of this substance be found overlying the debris of human occupancy, the merest tyro can see that the time since man occupied the cave can be equated with that which nature has taken to deposit the stalagmite—a problem which the chemist has often assayed to solve.
The characteristic flint implements of the drift are only sparingly met with in the earlier caverns frequented by man. Now it is a remarkable fact that there is very little difference, either in type or technique, between the implements of the earlier and later river gravels. On the other hand, those found in the caverns are all more or less different according to their antiquity, thus disclosing progressive skill and greater power of execution on the part of their makers. It has, therefore, been conjectured that few of the caverns were inhabited by man as early as the time when the first flint-bearing gravels were deposited. In these days the few nomadic specimens of humanity were content to wander along the streams and woods in search of fruits, buds, and the smaller animals, of which there was an ample supply. The coup-de-poing was, under the circumstances, sufficient to supply all their wants, more especially as they required neither houses nor garments. The usefulness of this primitive implement led to its long continuance, as a sine qua non, in the simple armoury of these early representatives of humanity.
Classification of Materials.
In the absence of positive chronology, every student of the prehistory of man will recognise the necessity of having some convenient method of tabulating the phenomena described in their order of succession, as geologists have so successfully done by collating fossils and other organic remains with the superposition of strata. In prehistoric archæology various methods
