The hill known as Ord Hill of Kissock is crowned, as is Craig Phœdrick, with ruins still standing, but the vegetation about them is so dense and thorny that it is difficult to make out the condition of the remains. The ruins, which can only be seen from one side, appear however to have formed part of fortifications, dating from the same time and serving the same purpose as those of Craig Phœdrick. Were they forts? There is certainly no sign of their having been used as habitations. Or were they, as some archæologists are disposed to think, beacon houses used for warning the people of the approach of the Norman pirates or Scandinavian Vikings, whose depredations were not discontinued until the eighth century of the Christian era? Hypotheses are always easy, but proofs of these hypotheses are difficult to find, and we confess we have none to bring forward.[33]
Passing to France, we find the greater number of vitrified forts in the Département de la Creuse. At Châteauvieux is an enceinte of oval form, 416 feet wide at its broadest part.[34] An earthwork, 22 feet wide at the base, serves as foundation to a wall, the outer and inner portions of which consist of small granite stones, arranged in regular layers. The space between the two series of small stones is filled in with a sheet of melted granite, some twenty-four inches wide, resting on calcareous tufa. The whole mass is completely vitrified, and regular geodes or nodules lined with crystals and draped with pendent drops of melted rock have been produced.
The ancient fortress of Ribandelle, of circular form, rises above the Creuse, opposite Châteauvieux. It was successively occupied by the Celts, the Romans, and the Visigoths, but we are unable to fix the date of its erection or the name of the people who built it. There remain but a few ruins at the present day, but we can make out in them the same mode of construction as that followed at Châteauvieux. The walls are faced with unhewn stones, the outer side of which still retains a natural appearance, while the inner is corroded and disintegrated. In the wall itself, separated from the facings by beds of peat mould, are great blocks of vitrified granite. The traces of the action of fire are specially noticeable in the upper part of the walls, so that they were evidently finished when the fusion took place.
The site of the furnace in these forts is difficult to determine. It was evidently not situated under any of the blocks, for the earthworks on which they rest retain no traces of the action of fire. Nor was it situated at the side, for the outer facings have retained alike their original form and consistency. Nor can the furnace have been lit on the blocks, as heat exercises its action by radiating in every direction. We are therefore forced to the conclusion that the fire was spread with the aid of spaces left in the inside of the construction at various points, for the vitrified mass is divided into blocks, about nine and three fourths feet long, at very short distances from each other.
These few examples will be enough to give some idea of the strange vitrified forts. Many of them retain traces of Roman. occupation. The Guéret Museum possesses a fragment from the Ribandelle walls in which a Roman tile is completely imbedded; and M. Thuot picked up other tiles in a similar condition amongst the ruins. This is a very decided proof that the vitrification took place after the arrival of the conquerors of Gaul. The weapons and tools discovered would appear to confirm this idea, and to suggest similar explanations of vitrification elsewhere. If so, we shall have to admit that vitrified forts date from the earliest centuries of the Christian era, and are not prehistoric at all. We have, however, noticed them here on account of the grave doubts in the matter, and because they furnish a striking and valuable illustration of the relations existing from the most remote tunes between widely separated races, and maintained until the present time. In no other way can we account for the practice of the extremely difficult and complicated operation of the vitrification of bard rocks in districts so far apart as Norway and Scotland, Germany and the midlands of France.
The more we think of the difficulties vitrification presents, the greater is our astonishment. How was the fusion achieved of elements so refractory alike in their structure and in the resistance offered by accumulated masses of material? By what processes was heat brought up to the 1300 degrees necessary for the fusion of granite? The incineration and fusion of the materials of which the vitrified forts are made, especially the granite ones of La Creuse and the Côtes du Nord, bear witness, says Daubrée, to a surprising skill and knowledge of the management of fire in those who burned them, but these qualities were manifested also in extremely ancient metallurgical operations. It is quite impossible to suppose the vitrification to have been the result of a conflagration. No fire, whether accidental or the work of an incendiary, could be powerful enough to produce such results. The use of petroleum in the most terrible conflagrations of our own time—those of the Commune in 1871, for instance—did calcine and disintegrate stone, but I know of no case of vitrification.
The Keramic Museum of Sèvres contains several specimens which present very notable differences to each other. Those from Château-Gontier are formed of very close-grained quartzite granite of a greenish color streaked with black. The conglomerate welding there together is a vitrified scoria full of very small bubbles made by the escape of gas which had not had sufficient strength to get out. The block from Sainte-Suzanne (Mayenne) consists of quartz mixed with half calcined grains of feldspar, bleached by the action of fused glass, which once introduced filled up as it congealed all the vacant spaces with a vitreous substance of light greenish-white color. The fractures are green and bright, and are dotted with white points, which are all that is left of the stones after their disintegration in the grip of a heat that was alike intense and rapid in its action. The fragments brought from Scotland differ from those just described. They consist of small pieces of granite completely merged in a thick paste with which they form the mass, the whole breaking together when it does break; and the melted matter seldom has any bubbles in it.[35]
The process employed in cementing the materials of the vitrified forts was then perfectly unique. The processes employed to obtain the necessary heat varied according to circumstances and according to the nature of the materials used. At Sainte-Suzanne and at La Courbe marine salt was used as a flux. Captain Prévot[36] thinks that the walls were smeared with a coating of clay, and that as in the baking of bricks spaces were left between so as to produce more intense heat. M. de Montaiglon is of opinion that the buildings were in the first instance erected without the use of any calcareous or argillaceous material, and that glass in a state of fusion was poured over them afterwards, this glass consolidating them and forming with them one indestructible mass. M. Thuot seems much disposed to share this last opinion, but he thinks that some chemical materials such as soda or potash were also used. Yet one other possible solution may be mentioned, a solution which is becoming more and more generally accepted, namely that the granite was not after all really melted, but that the vitrification should either be attributed to the fusion of the argillaceous mass, which has been subjected to an igneous transformation, such as that which often takes place in furnaces for baking bricks and in lime-kilns.[37]
Whatever explanation we may accept, however, the processes employed certainly bear witness to a much more advanced state of civilization than was acquired in the earliest ages of humanity. We have been led by the great interest and mystery of the subject to dwell longer on it than we intended, and we must hasten to return to prehistoric times with a determination not to transgress again.
Fortifications are a proof of combined action leading to a common end; they imply social organization, chiefs to command, workmen to obey. A recent discovery enables us to form a very accurate picture of prehistoric men gathered together not only for purposes of defence, but in a society already rich, industrious, and, if we may so speak, learning to cultivate the arts of peace.