The area described is the eastern coast of the northern, or Russian, part of Sakhalin Island. The surface features are grouped in lagoon, terrace, hill, and mountain zones. Lagoon formation is particularly discussed as being caused in part by coastal upheaval, formation of sand bars, and lines of faulting. The formations exposed in the oil districts are shales, sandstones, and conglomerates of Tertiary age, grouped in lower, middle, and upper divisions, partly on a physical and partly on a fossil basis. The general strike of the region is north-south, parallel to the coast. Seven main anticlines are marked by pronounced dips and by oil seepages and asphalt beds. Considerable drilling has been done, both by primitive methods and by diamond-drilling, cable tools, and rotary rigs. In the first half of 1925, three or four wells in the Oha field produced 41,741 barrels of oil. An analysis of oil from a depth of 180 meters shows no gasoline. One test well reached a depth of 1,504 meters; at 879 meters 20 barrels of oil were found, and at 1,227 meters 200,000 cubic feet of gas blew out.