Group at Liberty (Ohio).
Figure 87.
Trenches at Juigalpa (Nicaragua).
We must not omit to name an extraordinary system of intrenchments at Juigalpa, in Nicaragua, which so far as I know is quite unique. This is a series of trenches extending for several miles ([Fig. 87]), varying in width from nine and a half to thirteen feet; at equal distances are oval reservoirs, the longest axis of which measures as much as seventy-eight feet. In each reservoir are two or four mounds, probably serving as watch-towers. We know nothing either of the people who erected these singular structures or of the enemy from whom they formed a protection. Nor can anything be guessed as to the way in which the defence was conducted. All is involved in obscurity, and at every turn we are compelled to repeat that prehistoric studies are weighted with uncertainty, long and arduous study being necessary to bring ever so little order into the chaos in which everything connected with them is involved.
We must cursorily refer to some other fortifications which really scarcely belong to our subject, though certain archæologists claim for them a prehistoric origin. We refer to the vitrified forts, which are strange structures in which stones, such as granite and gneiss, quartzite and basalt, have been subjected to a heat so intense as to produce vitrification.
These vitrified forts are enceintes, generally of round or elliptical form, carefully erected where they were most needed for defence, and protected by one or more ramparts.[28] The ramparts all bear traces of vitrification, more or less complete, which has, so to speak, cemented them together. The vitrification is very unequal, being complete in some parts and scarcely noticeable in others. It is evident that the builders did not know how to direct their fire uniformly.
Ever since 1777 vitrified forts have been known in Scotland, and until 1837 they were supposed to exist nowhere else. About that time, however, Professor Zippe called attention to similar ruins in Bohemia, and later it was announced that discoveries of the same kind had been made in various parts of France, Denmark, and Norway. Virchow speaks of the Schlaken Wälle, or ramparts of vitrified scoria, near Kern[29] and Schaafhausen, and gave an account of them at a meeting of German naturalists at Ratisbon. It would be easy to multiply instances. Vitrified walls are known in the Puy-de-Dôme, in which the facing is of clay, and draught flues, for regulating and fanning the flames, have been made out. At Castel-Sarrazin is a camp refuge with similar dispositions,[30] and recently Daubree presented to the Académie des Sciences a piece of porphyry artificially vitrified from the prehistoric enceinte of Hartmannswiller Kopf in Upper Alsace.[31]
It is in Scotland, however, that are situated the most remarkable vitrified forts. A few years ago no less than forty-four were counted. The most celebrated are those of Barry Hill and Castle Spynie in Invernesshire, Top-O-Noth in Aberdeen, and a small fort which rises from a lofty rock in the midst of the Strait of Bute. Vitrified cairns also occur in the Orkney Islands, notably on the little isle of Sanday, but the most interesting structures of the kind are Craig Phœdrick and Ord Hill of Kissock, which rise up like huge pillars on the hills at the entrance of Moray Firth, at a distance of three miles from each other.[32]
Craig Phœdrick is now covered with a luxuriant vegetation of broom, furze, and fern, with groves of firs and larches, amongst which the explorer makes his way with difficulty to the fortifications, or rather to the piles of massive blocks to which that name has been given. These blocks form an acropolis of oval form, the upper part of which is a flat terrace encircling a central basin some six and a half to nine and a half feet deep, which may be compared to the craters of the extinct volcanoes of Auvergne. The sides of the mound are strewn with cyclopean blocks of vitrified granite, which evidently originally formed part of the fortifications. It is on the eastern side, overlooking the valley of the Ness, that the buildings are of the greatest importance; two terraces can be made out, the lower projecting beyond the upper, forming a double series of almost perpendicular fortifications, constructed of vitrified blocks cemented together with thin layers of mortar, spread without any attempt at regularity. The blocks form, with the mortar, a conglomerate so compact that when struck with a hammer they break without separating. Examination of fragments under the microscope prove that they have gone through important mineralogical transformations, under the influence of what must have been an extremely high temperature. The heat must have been indeed intense which could cause mica to disappear entirely, and feldspar to melt almost completely.