on all their disciples. This is the one saving doctrine of druidism, which thus prepared the way for Christianity. There were Druids amongst all the Celtic tribes of France, Britain, and Ireland. The British Druids in the time of Cæsar were very famous both as priests and scholars; so that it was customary for the young Druids of Gaul to be sent over to Britain to finish their education in the colleges of the British Druids. Their chief establishment was in the Island of Anglesey, anciently called Mona; so at least it is called by Tacitus, although Cæsar seems to give that name to the Isle of Man. During the period immediately preceding the arrival of St. Patrick in Ireland, it seems highly probable that Mona was occupied by a colony of the Irish Celts. It is certain, at least, that very frequent and friendly intercourse took place between Ireland and Anglesey, from which it may be safely inferred that if the druidism of Anglesey was not of Irish origin, Irish as well as Gaulish Druids were certainly educated in that island. The Druids worshipped not in temples made with hands. As in Palestine, and many Eastern countries, these pagan priests conducted their religious services in 'groves' and 'high places' under the shade of the spreading oaks, from which some writers derive their name--_derw_ being the Celtic, not the Greek name for oak. Hence this tree was sacred in their eyes; their dwellings were surrounded with oak groves, whose dark foliage threw a sombre and solemn shade over the rude altars of unhewn stone on which they offered their sacrifices. The yew, blackthorn, and quicken were also regarded as sacred trees, at least by the Irish Druids, who made their divining rods in some cases from the yew, but oftener from oaken boughs. The mystic ogham characters were also cut by the Druids on staves made from the yew, at least so we are informed in some of our oldest Irish tales.[6]