A couple of generations ago there were laid down the main divisions of successive ages of stone, bronze, and iron; and then the division of the stone age into palaeolithic and neolithic. After that followed the separation of palaeolithic into four main periods in France, more or less applicable to other lands. Further definition was yet found to be necessary, and the neolithic and bronze ages were marked off into many classes, which had to be distinguished by the names of places where they were first found; and thus we reach a multitude of names, such as Mycenaean, Hallstattian, the period of La Tène, etc. Such a piecemeal plan is well enough for a beginning; but it is not capable of exact definition, it is cumbersome, and it does not express the relation of one period to another.
Sequences.
Before we can think of subdividing a period into a continuous notation, the first requisite is to be able to place the material into its original order or sequence. Let us suppose some old country mansion, where it has been the habit to close permanently any room in which an owner had died, and leave everything in it undisturbed. If we went through such a series of rooms we could not doubt their order of date if we looked at their contents. The William IV room could not be put to the middle of George III’s reign; the George II room could not be supposed to go between those of James II and Anne. Each room full of furniture would have some links of style with that of the generation before, and of the generation after it, and no real doubt could exist as to the sequence of the whole series. What is true of a room full of furniture is equally true of a grave full of pottery. If we compare together a series of groups of pottery which are not separated by any long time, there will always be found some relationship between the forms in different groups: one group will be seen to fall between two others if it contains forms to be found in each of the other groups, though these others may have nothing in common together. A fragment of the alphabet, K L M N O P, must fall between H I J K L and O P Q R, and proves their connection.
Thus if each form lasted in use for a uniform length of time the problem would be fairly simple. But it is complicated by the plainer forms lasting far longer in use than the complex or highly decorated forms; some may go on being made for a thousand years, others may not have been made for even ten years. Hence it is needful to resort to various statistical modes of sorting, which differ in each case. A complete instance of the process is given in Diospolis Parva, pp. 4–8.
On the other hand, the sorting of material is greatly helped by any clear series of forms derived one from the other; especially a series of degradation, and reduction of useful elements to mere ornament. It is well, however, to have a check on one end of a series, by connecting it to known times, so as to prove which way it proceeds.
Sequence dates.
What notation should be used to express a series of sequences must vary with conditions. Where we can deal with a larger number—many hundreds—of good graves, each containing plenty of material, then a scale of equal numbers of graves is perhaps the fairest that can be taken. Thus for a scale of sequence dates, for the pottery named above, I adopted 50 numbers, each representing 20 graves.
The final result is to express the time-range of each type of pottery and of other objects in the graves in terms of the scale of sequence of the tombs. Thus the date of certain forms may be stated as 33–42 sequence date; 37–70 sequence date; 45–48 sequence date, etc. And when this is once established it is easy to date all further graves by arranging the dates of each object found in a grave, for instance in actual cases:—
| Sequence dates. | Sequence dates. | |
| 30–36 | 35–68 | |
| 32–68 | 60–69 | |
| 30–42 | 68–78 | |
| 31–34 | 68–78 | |
| Limits | 32–34 | 68 |
The larger the group the more closely it is dated, by reason of the various forms having a very small common ground of dating.