 The island is composed of a variety of volcanic and <unk> rock formations from the Devonian period . At that time the Scottish <unk> formed part of the Old Red <unk> Continent and lay some 10 @-@ 25 degrees south of the equator . The <unk> of Old Red <unk> , laid down from <unk> to 370 million years ago , were created as earlier <unk> rocks , <unk> by the formation of <unk> , eroded and then were deposited into river <unk> . The freshwater Lake <unk> existed on the edges of the eroding mountains , stretching from Shetland to the southern Moray Firth . The structure of Papa <unk> is largely made up of ashes and <unk> from volcanic activity associated with this period , including bands of solidified volcanic ash and <unk> ( <unk> ) , but there is also a Devonian fish bed at <unk> Banks . There are numerous large boulders deposited by Pleistocene <unk> . 
