Which "experiments to solve geological questions" did Berend George Escher use?

Question

Berend George Escher was a Dutch geologist (and half-brother of artist M. C. Escher). His Wikipedia page states that:

He was also a pioneer in using experiments to solve geological questions, for which he set up a laboratory in Leiden.

But there is no source to this claim¹. Encyclopedia.com has a bit more details:

Escher was the first geologist in the Netherlands to use laboratory experiments for the study of geological phenomena. His experiments in connection with salt domes were carried out with Kuenen (1929), who later used experimental methods in his sedimentological research. Experimental facilities designed by Escher served engineering purposes in the reclamation of the Zuider Zee.

And in the bibliography:

For the experiments on salt domes with Kuenen, see Leidse Geologisch Medelingen. 3 (1929, 151–181. A summary of most of Escher;s geological experiments is “Eine Übersicht der im geologischen Institut in Leiden von 1920 bis Ende 1937 ausgeführten geologischen Experimente,” in C. R. Congr. Int. de Géogr. Amsterdam. 2 (1938), 273–278.

But I could not find a digital copy of the latter source online, and even if I did, according to the title it will likely be written in German. So I'd like to ask:

Apart from the salt dome experiments, which geological experiments did Berend George Escher use to solve geological questions?

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¹ Following njuffa's answer, I've now added the proper reference to the Wikipedia article.

Answer 1

This question highlighted the importance of complete and accurate citations. I spent a couple of hours researching the exact details of the two publications mentioned, after which it took on the order of ten minutes to find scans of them. The first publication is:

B. G. Escher and Ph. H. Kuenen, "Experiments in Connection with Salt Domes." Leidse Geologische Mededelingen, Vol. 3, No. 1, 1928, pp. 151-182 (plus 18 additional plates). Scan available at Naturalis Biodiversity Center.

According to the abstract the goal of the work covered by this publication was to experimentally validate the Lachmann-Arrhenius-Harbort theory that salt domes are formed by isostasy combined with the lower density and greater plasticity of salt compared to overlaying sedimentary layers. The modelling used layers of paraffin, clay, and gypsum acted upon by hydraulic presses. The experiments confirmed that the folding observed with salt domes can be fully explained by the Lachmann theory.

The proceedings of the 1938 conference turned out to be not only spread over two volumes, but the voluminous second volume was split into multiple fascicles, each covering one or more topical sections, such as cartography, physical geography, oceanography, etc. I found Escher's paper in the fascicle for section IIa:

B. G. Escher, "Eine Übersicht der im Geologischen Institut in Leiden von 1926 bis Ende 1937 ausgeführten geologischen Experimente." Comptes Rendus Du Congrès International de Géographie, Amsterdam 1938, Vol. 2, Section II a, Géographie Physique, pp. 273-278. The Delpher service of the Royal Library of the Netherlands provides a scan.

This publication provides an overview of seventeen experiments, seven of which have associated publications. Twelve of the experiments were water-centric, mostly having to do with flowing water and wave action, where the latter group was trying to replicate various features of coastal geomorphology and examined the action of waves upon levees to find optimal cross sections. The laboratory used an innovative combination of a water channel with a wind tunnel. One interesting experiment in the former group examined the role of underwater erosion in the formation of submarine canyons.

Of the remaining experiments, one dealt with the formation of ventifacts, with wind erosion modeled by sand being propelled by a re-purposed vacuum cleaner. Two experiments dealt with tectonics: the formation of salt domes and folding over liquid substrates, modeling involving layers of paraffin. Finally there were two experiments concerning volcanism. If I understand it correctly, one dealt with erosion processes during the formation of calderas (using canisters of compressed air to model escaping volcanic gasses), the other with depository processes during the formation of volcanic cones (using a vertical stream of sand propelled upwards by two back-to-back vacuum cleaners).