It is customary and obvious to divide Java into three divisions, the middle part of the island narrowing into a kind of isthmus, and each of the divisions thus indicated having certain structural characteristics of its own. West Java, which consists of Bantam, Krawang and the Preanger Regencies, has an area of upwards of 18,000 sq. m. In this division the highlands lie for the most part in a compact mass to the south and the lowlands form a continuous tract to the north. The main portion of the uplands consists of the Preanger Mountains, with the plateaus of Bandong, Pekalongan, Tegal, Badung and Gurut, encircled with volcanic summits. On the borders of the Preanger, Batavia and Bantam are the Halimon Mountains (the Blue Mountains of the older travellers), reaching their greatest altitudes in the volcanic summits of Gedeh and Salak. To the west lie the highlands of Bantam, which extending northward cut off the northern lowlands from the Sunda Strait. Middle Java is the smallest of the three divisions, having an area of not much more than 13,200 sq. m. It comprises Tegal, Pekalongan, Banyumas, Bagelen, Kedu, Jokjakarta, Surakarta, and thus not only takes in the whole of the isthmus but encroaches on the broad eastern portion of the island. In the isthmus mountains are not so closely massed in the south nor the plains so continuous on the north. The watershed culminating in Slamet lies almost midway between the ocean and the Java Sea, and there are somewhat extensive lowlands in the south. In that part of middle Java which physically belongs to eastern Java there is a remarkable series of lowlands stretching almost right across the island from Semarang in the north to Jokjakarta in the south. Eastern Java comprises Rembang, Madiun, Kediri, Surabaya, Pasuruan and Besuki, and has an area of about 17,500 sq. m. In this division lowlands and highlands are intermingled in endless variety except along the south coast, where the watershed-range forms a continuous breakwater from Jokjakarta to Besuki. The volcanic eminences, instead of rising in lines or groups, are isolated.