SABIIA - Sistema Aberto e Integrado de Informação em Agricultura (Sabiia)

During his second Karakoram expedition in 1925 Mr. Ph. C. Visser collected some 70 rock specimens from the valley of the Hunza and its tributaries. The following is a petrographic description of these specimens and I gladly take this opportunity of thanking Mr. Visser for entrusting me with his valuable material. Geologists are much endebted to this energetic explorer for bringing together such a considerable number of samples under circumstances in which all carriage had to be reduced to a minimum and when so many other calls were being made on his time and energy. A collection made by a layman and therefore taken without many observations on mode of occurrence, must naturally be of limited value. When, however, it concerns a region that is almost terra...

Note on Penck and Brückner's diagram of the fluvio-glacial series

Ano: 1928

URL: http://www.repository.naturalis.nl/record/505796

In their classical studies on the Alpine glaciation Penck and Brückner gave a small blockdiagram to illustrate the arrangement and shape of the deposits at the lower end of a former glacier: the fluvioglacial series. This diagram has been reproduced in so many text-books, that it may be worth-while pointing out a fault in its construction. The case represented by the authors is that of two terminal amphitheatres lying within eachother (fig. 1) 1). The manner in which the outer moraine with its fluvio-glacial fan of sediments is drawn in on top of the inner moraine proves it to be the younger of the two. In this case the glacier must have ridden over the inner circle, thereby destroying its ridge; but in the drawing this ridge is represented as having been...

Experimental investigation into the mechanism of folding

Ano: 1926

URL: http://www.repository.naturalis.nl/record/505947

Kuenen, Ph.H.; Sitter, L.U. de.

The investigation of geological structures due to folding led de Sitter to form an opinion on the mechanical problems involved (Bibl. 7). His principal contention is that in simple cases the relative movements of particles with respect to eachother during deformation leading to a fold, have been purely concentric. During such concentric deformation all layers maintain their original thickness and length over the whole profile. All differential movements of neighbouring particles are parallel and therefore concentric. Towards the core of the anticlines and deeper down in the crust the geometrical relations, as construction will show, necessitate a deviation from this principle and either thrusting or plastic thickening of the rocks must take place. The...

Experiments in connection with Salt Domes

Ano: 1938

URL: http://www.repository.naturalis.nl/record/505864

Escher, B.G.; Kuenen, Ph.H..

The different theories concerning the origin of Salt Domes in Roumania, Germany, Texas, Louisiana, Colorado and Utah are discussed. In Roumania the salt occurs in cores of “Diapir” anticlines. The existance of hills of salt indicates, that the salt is still pushing upwards. In Germany the salt district shows slight folding but the salt itself is intensively folded. The theory of Lachmann-Arrhenius-Harbort explains the salt domes by isostasy combined with a lower specific gravity and greater plasticity of the salt than of the covering layers. This theory is opposed by Stille, who accounts for the salt domes by mesozoic folding. The latter theory has apparently gained preference in America for the explanation of the Salt Domes in Texas and Louisiana,...

Contributions to the geology of the East Indies from the Snellius expedition

Ano: 1928

URL: http://www.repository.naturalis.nl/record/505826

The oceanographical expedition on board Hr. Ms. Willebrord Snellius spent 15 months in investigating the eastern part of the Netherlands East Indies from 1929 to 1930. The present author accompanied the expedition as geologist. The geological results of the expedition may be devided into two parts. The first comprises those subjects that stand in direct relationship to the oceanographical work of the expedition, viz: the geological interpretation of the bathymetrical data obtained, the geology of coral reefs and the bottomsamples. These subjects are to be dealt with in the reports of the expedition. Two volumes have already appeared:

Experiments in connection with Daly's hypothesis on the formation of submarine canyons

Ano: 1935

URL: http://www.repository.naturalis.nl/record/505823

Shepard has made us familiar with the shape and various properties of submarine gorges and in a number of publications he has shown the great importance to earth-science of these wonderful features of the sea floor. Various hypotheses have been brought forward to explain the formation of submarine canyons. The only hypothesis to which there are no grave objections, is that suggested by Daly. During the low sea levels of the ice age mud was stirred up on the shallowing shelves and the dense water ensuing, flowed down the continental slopes, gradually eroding the gorges. This theory can be substantiated by experiments. These proved that a suspension will flow down a slope without being much diluted by mixing, that such a flow will concentrate in slight...

The Porphyry District of Lugano, West of the Valganna

Ano: 1937

URL: http://www.repository.naturalis.nl/record/505608

During an excursion to the South of Switserland, Professor Escher suggested my mapping out the south-western corner of the porphyry district of Lugano. I gladly agreed, for his detailed examination of the Morcote-peninsula had already shown that many interesting facts had escaped unobserved during the small-scale mapping forty years ago; and it was, therefore, highly probable that the projected work would prove fruitful. The necessary field-work was carried out in the spring of the years 1924 and 1925. The collected material I examined in the geological museum of Leiden, where it will remain in future.

Ano: 1925

URL: http://www.repository.naturalis.nl/record/505931

Pitted pebbles

As early as 1863 Sorby proved that pitted pebbles are the result of solution at the points of mutual contact in a conglomerate. As cause he suggested solution under pressure in saturated, stagnant groundwater by what has afterwards been designated Riecke’s principle. By the examination of polished cuts through a pitted conglomerate I found confirmation of this hypothesis. The alternate explanation by Daubrée, Kumm and others of solution in water held by capillarity at the points of contact could not cause the observed shapes of the pits. The experiments they used to disprove Sorby’s view are fundamentally incorrect. They attempted to form pits by a solvent liquid, instead of using pressure and saturated water. Groningen, November 1942.

Experiments on the formation of windworn Pebbles

Ano: 1942

URL: http://www.repository.naturalis.nl/record/505905

The influence of the wind laden with sand in modelling pebbles is believed by some authors to be only that of polishing the surface, by others of rounding off bits of stone that already possessed edges and corners, or again by others of wearing any fragment either rounded or angular into definite forms with ridges and facets, dependent on the shape of the basis (Alb. Heim). Experiments, fully confirming the last opinion, are described in this paper: no rounding off took place, while the models were slowly revolved in the sandblast, and vertical planes took on a backward slanting position, cutting eachother along sharp edges. Where sand corrosion is great, as in the desert, the windworn pebbles owe their shape to the laws formulated by Heim; many of the...

Ano: 1928

URL: http://www.repository.naturalis.nl/record/505808

K. Martin als docent

Een buitenstaander, die nu Martin ontmoet, zou moeilijk te overtuigen zijn, dat de onverbiddelijke wet al tien jaar geleden decreteerde, dat deze „jonge man” toen reeds te oud was om nog als docent aan de Leidsche universiteit op te kunnen treden. Maar als deze buitenstaander, zelf student, dan tevens hoorde, dat tijdgenooten van zijn eigen grootvader reeds bij Martin op de collegebanken zaten, dan zou hij realiseeren, dat als er ooit iemand zijn tijd uitgediend heeft, dit Martin is. Bijna een halve eeuw is hij aan het onderwijs aan de Leidsche universiteit verbonden geweest. Degenen, die het voorrecht gehad hebben het laatste jaar, dat hij doceerde, college bij hem te loopen, weten, dat hij tot op het laatst de enthousiaste redenaar gebleven is. Martin is...

Experiments on the formation of volcanic cones (In connection with East Indian volcanic islands)

Ano: 1931

URL: http://www.repository.naturalis.nl/record/505686

Several investigators have tackled the problem of the main causes that produce the slopes of volcanic cones, especially with a view to explaining the characteristic concave profiles of strato-volcanoes *). A satisfactory result has not been arrived at, however. This became evident to the present author while studying the submarine slopes of volcanoes in the East Indies. A number of submarine sections of isolated volcanic piles were constructed from the echo-soundings of the Snellius Expedition and from the data contained in the fair sheets of the Hydrographical Survey. These sections combined with the corresponding subaerial profiles will be reproduced in the Scientific Results of “the Snellius Expedition, Volume V: Geology, Part 1: Geological...

Experimental abrasion of pebbles I. Wet sandblasting

Ano: 1933

URL: http://www.repository.naturalis.nl/record/505966

Pebbles of various kinds were subjected to abrasion by a sand-laden current of water. The loss in weight resulting from the action of coarse and fine sand at different velocities was measured. There proved to be no abrasion below a velocity of 70 cm per second. At a bottom velocity of this amount medium to large pebbles are already rolled along. This causes much severer loss of weight. Hence wet sandblasting is not important for particles under cobble size either in streams or on beaches.

Petrografic description of some igneous rocks from the Cordillera of South Mendoza, in the Argentine

Ano: 1955

URL: http://www.repository.naturalis.nl/record/505758

Comparatively little is yet known of the intricate igneous history of the Cordillera of South Mendoza. Almost all the knowledge we have is due to the field- and stratigraphical work of Dr. H. Gerth of Leiden (bibl. 1 and 2), and the petrographic studies of Dr. H. G. Backlund (bibl. 3 and 4) on the material collected by the former investigator. A part of this material, however, had remained unexamined at Leiden, and at the request of Dr. Gerth Dr. L. U. de Sitter began an examination of the 25 slides prepared. After a provisional examination and the determination with the universal stage 1) of some plagioclases in most of the slides that were not too much decomposed Dr. de Sitter left Leiden for Dutch East India. Dr. Gerth was so kind as to allow me the...

The negative isostatic anomalies in the East Indies (with Experiments)

Ano: 1926

URL: http://www.repository.naturalis.nl/record/505659

In this paper a series of experiments is described relating to the deformation of the earth's crust by horizontal compressive stress. A floating model crust is compressed in most cases, after a slight dent has been run across it to represent a geosyncline. When materials of the correct order of strength are used, the crust buckles down below the model geosyncline forming a root at the lower surface of the crust. At no time in this process is a topographic depression formed at the surface that exceeds the depth of deep-sea troughs as compared to the thickness of the earth's crust. Other possibilities suggested by the experiments are that the crust may break through and overthrust and that a broad geosyncline will surmount a more complicated form of root. It...