|Yorkshire is the largest county in the United Kingdom. Within the borders of the historic county of Yorkshire are areas which are widely considered to be among the greenest in England, due to the vast stretches of unspoiled countryside in the Yorkshire Dales and North York Moors and to the open aspect of some of the major cities. Historically, Yorkshire was divided into three ridings and the Ainsty of York. The term 'riding' is of Viking origin and derives from Threthingr meaning a third part. The three ridings in Yorkshire were named the East Riding, West Riding and North Riding. The East and North Ridings of Yorkshire were separated by the River Derwent and the West and North Ridings were separated by the Ouse and the Ure/Nidd watershed. In 1974 the three ridings of Yorkshire were abolished and York which had been independent of the three ridings, was incorporated into the new county called North Yorkshire. In Yorkshire there is a very close relationship between the major topographical areas and the geological period in which they were formed. The Pennine chain of hills in the west is of Carboniferous origin. The central vale is Permo-Triassic. The North York Moors in the north-east of the county are Jurassic in age while the Yorkshire Wolds to the south east are Cretaceous chalk uplands. The countryside of Yorkshire includes the North York Moors and Yorkshire Dales National Parks, and part of the Peak District National Park. Nidderdale and the Howardian Hills are designated Areas of Outstanding Natural Beauty. Spurn Point, Flamborough Head and the coastal North York Moors are designated Heritage Coast areas, and are noted for their scenic views with rugged cliffs such as the jet cliffs at Whitby, the limestone cliffs at Filey and the chalk cliffs at Flamborough Head. Scarborough is Britain's oldest seaside resort dating back to the spa town-era in the 17th century, while Whitby has been voted as the United Kingdom's best beach, with a "postcard-perfect harbour".