Question: What distinctive surface is the historic Merton Street, that runs parallel to High Street in the southeastern university city of Oxford, England?

full_context: Document 1: Exeter: Exeter ( ) is a cathedral city in Devon England with a population of 129,800 (mid-2016 est. ). It lies within the county of Devon, of which it is the county town as well as the home of Devon County Council. The administrative area has the status of a non-metropolitan district under the administration of the County Council; a plan to grant the city unitary authority status was scrapped under the 2010 coalition government. The city is on the River Exe about 37 mi northeast of Plymouth and 70 mi southwest of Bristol.
Document 2: Alfred Street: Alfred Street is a street running between the High Street to the north and the junction with Blue Boar Street and Bear Lane at the southern end, in central Oxford, England. To the south is Christ Church, one of Oxford University's historic colleges.
Document 3: Eastgate Hotel: The Mercure Eastgate Hotel (aka The Eastgate locally) is a hotel located in the historic university city of Oxford, England. It is located on the south side of Oxford's High Street near to the Ruskin School of Drawing and Fine Art and the Examination Schools of Oxford University.
Document 4: Queen's Lane: Queen's Lane is a historic street in central Oxford, England, named after Queen's College, to the south and west. St Edmund Hall, a constituent college of the University of Oxford, is located on the southern end of this street.
Document 5: University of Oxford: The University of Oxford (informally Oxford University or simply Oxford) is a collegiate research university located in Oxford, England. It has no known date of foundation, but there is evidence of teaching as far back as 1096, making it the oldest university in the English-speaking world and the world's second-oldest university in continuous operation. It grew rapidly from 1167 when Henry II banned English students from attending the University of Paris. After disputes between students and Oxford townsfolk in 1209, some academics fled north-east to Cambridge where they established what became the University of Cambridge. The two "ancient universities" are frequently jointly referred to as "Oxbridge".
Document 6: Monk Street, Monmouth: Monk Street is an historic street in the town of Monmouth, Monmouthshire, Wales. A portion of it was in existence by the 14th century, and appears on the 1610 map of the town by cartographer John Speed. It runs in a north-south direction, extending northward from its intersection with Whitecross Street. The name of the street relates to the nearby Priory, as well as the gate which was originally on this road and provided part of the town's defences, Monk's Gate. Monk Street is lined with numerous listed buildings.
Document 7: Oxford-Cambridge Arc: The Oxford-Cambridge Arc is a notional arc of agricultural and urban land at about 75km (about 50 miles) radius of London, southern England. It runs between the two English university towns of Oxford and Cambridge via Milton Keynes and other important settlements in Cambridgeshire, Bedfordshire, Buckinghamshire and Oxfordshire, at the northern rim of the London commuter belt. It is significant only in economic geography, with little physical geography in common.
Document 8: South East England: South East England is the most populous of the nine official regions of England at the first level of NUTS for statistical purposes. It consists of Berkshire, Buckinghamshire, East Sussex, Hampshire, the Isle of Wight, Kent, Oxfordshire, Surrey and West Sussex. As with the other regions of England, apart from Greater London, the south east has no elected government.
Document 9: Oxford: Oxford ( ) is a city in the South East region of England and the county town of Oxfordshire. With an estimated 2015 population of 168,270, it is the 52nd largest city in the United Kingdom, and one of the fastest growing and most ethnically diverse. The city is situated 57 mi from London, 69 mi from Bristol, 65 mi from both Southampton and Birmingham and 25 mi from Reading.
Document 10: Dead Man's Walk, Oxford: Dead Man's Walk (or Deadman's Walk) is a footpath running east–west in central Oxford, England, situated immediately to the south of Merton College and just outside the old city wall, with Corpus Christi College at the western end. To the north, Grove Walk connects with Merton Street through a gateway. Immediately to the south is Merton Field with Merton Walk connecting to the wide tree-lined Broad Walk, which runs parallel with Dead Man's Walk. Beyond that is Christ Church Meadow.
Document 11: Oxford, Maine: Oxford is a town in Oxford County, Maine, United States. The population was 4,110 at the 2010 census. Oxford is home to the Oxford Plains Speedway, the annual Oxford County Fair, and Oxford Casino. The town includes the village of Welchville.
Document 12: Merton Street tennis court: Merton Street tennis court is the home of the Oxford University Real Tennis Club. It stands on the north side of Merton Street in central Oxford, England, and forms part of Merton College.
Document 13: Bristol: Bristol ( ) is a city and county in South West England with a population of 454,200 in 2017. The district has the 10th-largest population in England, while the Bristol metropolitan area is the 12th-largest in the United Kingdom. The city borders North Somerset and South Gloucestershire, with the cities of Bath and Gloucester to the south-east and north-east, respectively.
Document 14: Cambridge: Cambridge ( ) is a university city and the county town of Cambridgeshire, England, on the River Cam approximately 50 mi north of London. At the United Kingdom Census 2011, its population was 123,867, including 24,488 students.
Document 15: Merton Street: Merton Street is a historic and picturesque cobbled street in central Oxford, England. It joins the High Street at its northeastern end, between the Ruskin School of Drawing and Fine Art (together with the Examination Schools) and the Eastgate Hotel at the historic east gate of the city. It then runs east-west, parallel and to the south of the High Street for most of its length.
ground_truth: cobbled