Bog oak became popular in the making of jewellery in particular between 1860 and 1890. The fossilized wood was found in the peat marshes and bogs of Ireland where it turned hard enough to be carved into jewellery which became the height of fashion. It was a competitor to the jet industry founded at Whitby in the UK. This is a large example measuring 6.5cms x 5cms. There is a the carving of either an abbey or part of a castle. On the back is the original and traditional long pin with C clasp. The name Glena has been imprinted in to the back. That is an Irish girls name meaning "Valley of the army" Glenairm is a village in County Antrim, Northern Ireland.  It was apparently quite a tradition to have the original owners name imprinted to the back of the brooch. A lovely historic piece now well over a hundred years old and in remarkably good condition. Gift boxed by Vintageonline.