Setting aside these conclusions, in so far as they are merely conjectural, it appears established that the area over which these deposits of silver ornaments are found is limited to the three Scandinavian countries and the British Isles. It is certain that among the ornaments so found some are distinctively Scandinavian, and others distinctively Celtic, while the remainder, which constitutes the bulk of the deposits, is of unknown derivation, but has been conjecturally assigned to an Oriental origin, on account of its association with the Cufic coins. I therefore proceed to the examination of these objects which are of undetermined origin, with the view of ascertaining the special characteristics and relations of their form and ornament.
I have already remarked that the form of these bulbous brooches is that which is distinctive of the Celtic brooch—penannular, with expanded ends. Its special peculiarities are exaggerations of the specialties of form by which the Celtic type is distinguished from all others; and in this respect the form assumed by these bulbous brooches, though Celtic in type, is so strongly differentiated from the purely Celtic form, that it may be regarded as a distinct variety. No other form of brooch is so huge and massive, with such a length of pin. The Celtic brooch-maker was so much more of an artist than the mere silversmith that he flattened the ring of the brooch and broadened its terminal expansions in order to provide space for the elaborate surface decoration in which he delighted. The maker of these bulbous brooches, on the other hand, is so much more of the silversmith than of the artist that the bulk of his work is merely finished with the hammer—the ring and the pin are beaten into form, and the expansions made globular instead of flat. The form of these brooches, therefore, agrees with the Celtic form in its main features, its penannular character, and its length of pin, loosely looped on the ring of the brooch.
But if the form of these brooches be thus closely allied to the Celtic form, their ornament is no less closely allied to the Celtic system of ornamentation. The peculiar prickliness of the bulbs, which is the most marked feature of their character, is not distinctively Celtic, but a suggestion of it is occasionally found on Celtic silver-work, as, for instance, on the almost globular head of a Celtic brooch in the National Museum, and on a gold brooch found near Coleraine.[49] But the reverse hemispheres of the bulbous terminations of the Skaill brooches, which present this prickly ornamentation on the obverse, are also decorated with engraved designs. These are of two varieties, simple interlaced ribbon patterns and zoomorphic patterns. The character of the interlaced work so closely resembles the Celtic style that it may be said to be more Celtic than Scandinavian. The character of the zoomorphic work, on the other hand, is more Scandinavian than Celtic, and is suggestive of the style and treatment of the designs on the Manx crosses, while it more closely resembles some of the more characteristic designs of the purely Scandinavian metal-work of the heathen time.