The East-Midland and West-Midland dialects of Middle English are intermediate between the Northern and Southern/Kentish extremes. In the West Midlands there is a gradation of dialect peculiarities from Northern to Southern as one moves from Lancashire to Cheshire and then down the Severn valley. This dialect has left modern descendants in the working- class country dialects of the area. The East-Midland dialect is much more interesting. The northern parts of its dialect area were also an area of heavy Scandinavian settlement, so that northern East-Midland Middle English shows the same kinds of rapid development as its Northern neighbor. But the subdialect boundaries within East-Midland were far from static: the more northerly variety spread steadily southward, extending the influence of Scandinavianized English long after the Scandinavian population had been totally assimilated. In the 13th century this part of England, especially Norfolk and Suffolk, began to outstrip the rest of the country in prosperity and population because of the excellence of its agriculture, and — crucially — increasing numbers of well-to-do speakers of East-Midland began to move to London, bringing their dialect with them. By the second half of the 14th century the dialect of London and the area immediately to the northeast, which had once been Kentish, was thoroughly East-Midland, and a rather Scandinavianized East Midland at that. Since the London dialect steadily gained in prestige from that time on and began to develop into a literary standard, the northern, Scandinavianized variety of East-Midland became the basis of standard Modern English. For that reason, East-Midland is by far the most important dialect of Middle English for the subsequent development of the language.