Continent world ultimately persisted with these being regarded as separate continents. From the late 18th century, some geographers started to regard North America and South America as two parts of the world, making five parts in total. Overall though, the fourfold division prevailed well into the 19th century. Europeans discovered Australia in 1606, but for some time it was taken as part of Asia. By the late 18th century, some geographers considered it a continent in its own right, making it the sixth (or fifth for those still taking America as a single continent). In 1813, Samuel Butler wrote of Australia
Mid-Continent oil province Mid-Continent oil province The Mid-continent oil field is a broad area containing hundreds of oil fields in Arkansas, Kansas, Louisiana, New Mexico, Oklahoma and Texas. The area, which consists of various geological strata and diverse trap types, was discovered and exploited during the first half of the 20th century. Most of the crude oil found in the onshore mid-continent oil field is considered to be of the mixed base or intermediate type (a mix of paraffin base and asphalt base crude oil types). The first commercially successful oil well drilled in what was to be called the Mid-continent Oil Field