Francis Hindes Groome's Ordnance Gazetteer for Scotland observes that the geography of the county can be seen as "falling into three divisions - hilly, gently rising, and flat". The higher areas are found to the south and west, particularly into the Renfrewshire Hills and to the border with Ayrshire, with large areas of moorland. The land slopes downward to the River Clyde with the River Cart (formed by the White Cart Water and Black Cart Water) and the River Gryffe, all of which eventually flow into the River Clyde, providing drainage to the lower parts of the area. In the west of Renfrewshire can be found a number of small bodies of water such as Loch Thom and the Gryfe Reservoir, with Barr Loch and Castle Semple Loch in the south. A number of smaller hills and lochs are in the south-east in the county, with the Dams to Darnley Country Park separating Newton Mearns and Barrhead with a number of artificially dammed lakes including Balgray Reservoir, Ryat Linn Reservoir and Waulkmill Glen Reservoir. The upper scenery of the county was described in the 1911 Encyclopædia Britannica as "somewhat wild and bleak" though descending into pastureland around the rivers. The north-east of the county is heavily urbanised and forms part of the Greater Glasgow conurbation. The geology of the Renfrewshire is notable for its volcanic origins. The traditional industries of Renfrewshire were noted for their variety and diversity. Weaving and associated trades were common in the county and Paisley became particularly notable for this industry. The Paisley pattern remains a symbol of the area and its weaving past to this day. Prior to the 19th century, weaving was largely a cottage industry which took place around the towns and villages of the county. The Industrial Revolution saw the emergence of large-scale mills, with many concentrating in Paisley. In the 1930s, around 28,000 people were employed in the Coats mills in the town. Greenock's coastal position made the county an early centre for overseas trade. Shipbuilding on the River Clyde, particularly at Renfrew and Port Glasgow became significant in the later part of the 19th century. These emerged into the Lower Clyde Shipyards. Of the industry, only Ferguson Marine Engineering in Port Glasgow remains today. Many of the county's traditional industries were driven by export strength, with examples such as sugar refining, foundry-work, rope-making, machine-making, mineral work and the manufacture of chemicals are all noted as significant to the economy of Renfrewshire in the 1880s Gazetteer for Scotland entry, with the central areas for commerce noted as being Greenock and Port Glasgow.