Jerry Norman estimated that there are hundreds of mutually unintelligible varieties of Chinese. These varieties form a dialect continuum, in which differences in speech generally become more pronounced as distances increase, though the rate of change varies immensely. Generally, mountainous South China exhibits more linguistic diversity than the North China Plain. In parts of South China, a major city's dialect may only be marginally intelligible to close neighbors. For instance, Wuzhou is about upstream from Guangzhou, but the Yue variety spoken there is more like that of Guangzhou than is that of Taishan, southwest of Guangzhou and separated from it by several rivers. In parts of Fujian the speech of neighboring counties or even villages may be mutually unintelligible.