Folds are marvellous features of mountain terrains, but despite extensive research, many fundamental problems have still not been solved. In terrains of sandstone, fold hinges are rarely straight lines but curved, forming a pattern characterized by doubly plunging, elliptical dome‐and‐basin structures. Such structures are an obvious manifestation of coeval or successive shortening deformation in two orthogonal principal directions in the horizontal plane. Based on an anatomic investigation of the fold pattern of sandstone beds at the rocky beaches of Saint‐Jean‐Port‐Joli (Quebec, Canada), we propose that the doubly plunging folds may result from a transition from a plane deformation to a constrictional deformation due to auxetic effects of quartz‐rich rocks. The sandstone beds possessed potentially such negative values of Poisson's ratio that, when placed under compression in one direction, they become contracted in the transverse direction, producing a series of doubly plunging folds. Further work is needed to approve or disapprove the interpretation.

中文翻译：

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在砂岩地形中形成双折褶的另一种解释

褶皱是山地的奇妙特征，但是尽管进行了广泛的研究，许多基本问题仍未解决。在砂岩地形中，折页铰链很少是直线，而是弯曲的，形成了以双重下沉的椭圆形圆顶和盆地结构为特征的模式。这种结构是在水平面中两个正交的主方向上同时或连续缩短变形的明显表现。根据对Saint-Jean-Port-Joli（加拿大魁北克）岩石海滩上砂岩层褶皱样式的解剖学调查，我们认为，从平面形变过渡到收缩形变可能会导致双重下陷褶皱由于富含石英的岩石的膨胀作用。砂岩床具有潜在的泊松比负值，当在一个方向上受到压缩时，它们会在横向方向上收缩，从而产生一系列的双折褶皱。需要进一步的工作来批准或不同意该解释。