24. Bonaire

Before the visit of Prof. Rutten and his students in 1930, only once geological investigations were made on Bonaire. These took place in 1885, when Prof. Martin paid a short visit to the island. Though the stay of Prof. Martin on Bonaire lasted only four days, he nevertheless succeeded in composing a rough scheme of the geology of the island. I am very glad and I count it as an honour to have the opportunity of prosecuting the work of Prof. Martin. A visitor to Bonaire must, even before reaching the road of Kralendijk, observe the great topographical difference between the northern and the southern part of the island. One does not say too much when one asserts that Bonaire consists of two totally different parts. Of these, the northern part is higher and largely dissected, the southern part is a very low and level country. From a geological point of view the northern part is by far the most important: whereas the southern part is entirely composed of young quarternary limestones, the higher northern part contains all the older formations. That does not alter the fact, however, that quarternary limestones are very spread in the northern part too. This higher northern part of Bonaire has a NW.—SE. direction, and one can say that it owes this direction to the oldest formation on Bonaire, of which the strata strike chiefly NW.—SE. This oldest formation which we, during our investigations on the island in the summer of 1930, under the leadership of Prof. Rutten, called the „Washikemba formation”, after the Plantation Washikemba in E. Bonaire, is for the greater part built up of volcanic rocks. The formation begins with diabasic rocks, among which one can distinguish diabases, amygdaloidal diabases and diabasic tuffs. In the western part of the Washikemba formation the diabasic rocks pass upward into less basic rocks, chiefly being porphyrites, amygdaloidal porphyrites and porphyritic tuffs. At the top of the formation diabasic rocks appear here again. Higher up in the eastern part of the formation porphyritic rocks are intercalated rather irregularly between the diabasic rocks. Among the older diabase and, to a much greater extent, at the top of the formation cherts and radiolarites are intercalated between the volcanic rocks, and here and there calcareous cherts and limestones are interstratified between the other rocks. Many of the tuffs contain a bigger or smaller quantity of radiolaria and small foraminifera.