Later , on the Berwickshire coast , he found Siccar Point . There was `` a beautiful picture of this junction washed bare by the sea '' , where 345 million year old Devonian Old Red Sandstone overlies 425 million year old Silurian greywacke . They then took a boat trip from Dunglass Burn east along the coast with the geologist Sir James Hall of Dunglass and at Siccar Point found what Hutton called `` a beautiful picture of this junction washed bare by the sea '' , where 345 million year old Devonian Old Red Sandstone overlies 425 million year old Silurian greywacke .