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.
For its area Java is one of the most distinctly volcanic regions of the world. Volcanic forces made it, and volcanic forces have continued to devastate and fertilize it. According to R. D. M. Verbeek about 125 volcanic centres can be distinguished, a number which may be increased or diminished by different methods of classification. It is usual to arrange the volcanoes in the following groups: westernmost Java 11 (all extinct); Preanger 50 (5 active); Cheribon 2 (both extinct); Slamet 2 (1 active); middle Java 16 (2 active); Murio 2 (both extinct); Lavu 2 (extinct); Wilis 2 (extinct); east Java 21 (5 active). The active volcanoes of the present time are Gedeh, Tangkuban, Prahu, Gutar, Papandayan, Galung-gung, Slamet, Sendor, Merapi,[1] Kalut (or Klut), Bromo, Semeru, Lamongan, Raung, but the activity of many of these is trifling, consisting of slight ejections of steam and scoriae.
The plains differ in surface and fertility, according to their geological formation. Built up of alluvium and diluvium, the plains of the north coast-lands in western and middle Java are at their lowest levels, near the mouths of rivers and the sea, in many cases marshy and abounding in lakes and coral remains, but for the rest they are fertile and available for culture. The plains, too, along the south coast of middle Java—of Banyumas and Bagelen—contain many morasses as well as sandy stretches and dunes impeding the outlet of the rivers. They are, nevertheless, available for the cultivation more particularly of rice, and are thickly peopled. In eastern Java, again, the narrow coast plains are to be distinguished from the wider plains lying between the parallel chains of limestone and between the volcanoes. The narrow plains of the north coast are constituted of yellow clay and tuffs containing chalk, washed down by the rivers from the mountain chains and volcanoes. Like the western plains, they, too, are in many cases low and marshy, and fringed with sand and dunes. The plains, on the other hand, at some distance from the sea, or lying in the interior of eastern Java, such as Surakarta, Madiun, Kediri, Pasuruan, Probolinggo and Besuki, owe their formation to the volcanoes at whose bases they lie, occupying levels as high as 1640 ft. down to 328 ft. above the sea, whence they decline to the lower plains of the coast. Lastly, the plains of Lusi, Solo and Brantas, lying between the parallel chains in Japara, Rembang and Surabaya, are in part the product of rivers formerly flowing at a higher level of 30 to 60 or 70 ft., in part the product of the sea, dating from a time when the northern part of the above-named residencies was an island, such as Madura, the mountains of which are the continuation of the north parallel chain, is still.
The considerable rivers of western Java all have their outlets on the north coast, the chief among them being the Chi (Dutch Tji) Tarum and the Chi Manuk. They are navigable for native boats and rafts, and are used for the transport of coffee and salt. On the south coast the Chi Tanduwi, on the east of the Preanger, is the only stream available as a waterway, and this only for a few miles above its mouth. In middle Java, also, the rivers discharging at the north coast—the Pamali, Chomal, &c.—are serviceable for the purposes of irrigation and cultivation, but are navigable only near their mouths. The rivers of the south coast—Progo, Serayu, Bogowonto, and Upak, enriched by rills from the volcanoes—serve abundantly to irrigate the plains of Bagelen, Banyumas, &c. Their stony beds, shallows and rapids, and the condition of their mouths lessen, however, their value as waterways. More navigable are the larger rivers of eastern Java. The Solo is navigable for large praus, or native boats, as far up as Surakarta, and above that town for lighter boats, as is also its affluent the Gentung. The canal constructed in 1893 at the lower part of this river, and alterations effected at its mouth, have proved of important service both in irrigating the plain and facilitating the river’s outlet into the sea. The Brantas is also navigable in several parts. The smaller rivers of eastern Java are, however, much in the condition of those of western Java. They serve less as waterways than as reservoirs for the irrigation of the fertile plains through which they flow.
The north coast of Java presents everywhere a low strand covered with nipa or mangrove, morasses and fishponds, sandy stretches and low dunes, shifting river-mouths and coast-lines, ports and roads, demanding continual attention and regulation. The south coast is of a different make. The dunes of Banyumas, Bagelen, and Jokjakarta, ranged in three ridges, rising to 50 ft. high, and varying in breadth from 300 to over 1600 ft., liable, moreover, to transformation from tides and the east monsoon, oppose everywhere, also in Preanger and Besuki, a barrier to the discharge of the rivers and the drainage of the coast-lands. They assist the formation of lagoons and morasses. At intervals in the dune coast, running in the direction of the limestone mountains, there tower up steep inaccessible masses of land, showing neither ports nor bays, hollowed out by the sea, rising in perpendicular walls to a height of 160 ft. above sea-level. Sometimes two branches project at right angles from the chain on to the coast, forming a low bay between the capes or ends of the projecting branches, from 1000 to 1600 ft. high. Such a formation occurs frequently along the coast of Besuki, presenting a very irregular coast-line. Of course the north coast is of much greater commercial importance than the south coast.
Geology.—With the exception of a few small patches of schist, supposed to be Cretaceous, the whole island, so far as is known, is covered by deposits of Tertiary and Quaternary age. The ancient “schist formation,” which occurs in Sumatra, Borneo, &c., does not rise to the surface anywhere in Java itself, but it is visible in the island of Karimon Java off the north coast. The Cretaceous schists have yielded fossils only at Banjarnegara, where a limestone with Orbitolina is interstratified with them. They are succeeded unconformably by Eocene deposits, consisting of sandstones with coal-seams and limestones containing Nummulites, Alveolina and Orthophragmina; and these beds are as limited in extent as the Cretaceous schists themselves. Sedimentary deposits of Upper Tertiary age are widely spread, covering about 38% of the surface. They consist of breccias, marls and limestones containing numerous fossils, and are for the most part Miocene but probably include a part of the Pliocene also. They were laid down beneath the sea, but have since been folded and elevated to considerable heights. Fluviatile deposits of late Pliocene age have been found in the east of Java, and it was in these that the remarkable anthropoid ape or ape-like man, Pithecanthropus erectus of Dubois, was discovered. The Quaternary deposits lie horizontally upon the upturned edges of the Tertiary beds. They are partly marine and partly fluviatile, the marine deposits reaching to a height of some 350 ft. above the sea and thus indicating a considerable elevation of the island in recent times.
The volcanic rocks of Java are of great importance and cover about 28% of the island. The eruptions began in the middle of the Tertiary period, but did not attain their maximum until Quaternary times, and many of the volcanoes are still active. Most of the cones seem to lie along faults parallel to the axis of the island, or on short cross fractures. The lavas and ashes are almost everywhere andesites and basalts, with a little obsidian. Some of the volcanoes, however, have erupted leucite rocks. Similar rocks, together with phonolite, occur in the island of Bavian.[2]
Climate.—Our knowledge of the climate of Batavia, and thus of that of the lowlands of western Java, is almost perfect; but, rainfall excepted, our information as to the climate of Java as a whole is extremely defective. The dominant meteorological facts are simple and obvious: Java lies in the tropics, under an almost vertical sun, and thus has a day of almost uniform length throughout the year.[3] It is also within the perpetual influence of the great atmospheric movements passing between Asia and Australia; and is affected by the neighbourhood of vast expanses of sea and land (Borneo and Sumatra). There are no such maxima of temperature as are recorded from the continents. The highest known at Batavia was 96° F. in 1877 and the lowest 66° in the same year. The mean annual temperature is 79°. The warmest months are May and October, registering 79.5° and 79.46° respectively; the coldest January and February with 77.63° and 77.7° respectively. The daily range is much greater; at one o’clock the thermometer has a mean height of 84°; after two o’clock it declines to about 73° at six o’clock; the greatest daily amplitude is in August and the least in January and February. Eastern Java and the inland plains of middle Java are said to be hotter, but scientific data are few. A very slight degree of elevation above the seaboard plains produces a remarkable difference in the climate, not so much in its mere temperature as in its influence on health. The dwellers in the coast towns are surprised at the invigorating effects of a change to health resorts from 300 to 1200 ft. above sea-level; and at greater elevations it may be uncomfortably cold at night, with chilly mists and occasional frosts. The year is divided into two seasons by the prevailing winds: the rainy season, that of the west monsoon, lasting from November to March, and the dry season, that of the east monsoon, during the rest of the year; the transition from one monsoon to another—the “canting” of the monsoons—being marked by
- ↑ This Merapi must be carefully distinguished from Merapi the Fire Mountain of Sumatra.
- ↑ R. D. M. Verbeek and R. Fennema, Description géologique de Java et Madoura (2 vols. and atlas, Amsterdam, 1896; also published in Dutch)—a summary with map was published by Verbeek in Peterm. Mitt. xliv. (1898), 24–33, pl. 3. Also K. Martin, Die Eintheilung der versteinerungsführenden Sedimente von Java, Samml. Geol. Reichsmus. Leiden, ser. i., vol. vi. (1899–1902), 135–245.
- ↑ On the 16th of November the sun rises at 5.32 and sets at 5.57; on the 16th of July it rises at 6.12 and sets at 5.57. The longest day is in December and the shortest in June, while on the other hand the sun is highest in February and October and lowest in June and December.
