a highly faulted and folded assemblage of Ordovician to Devonian limestones, dolomites, sandstones, shales, volcanoclastic strata, and igneous rocks; upper Paleozoic to Triassic sandstones and shales; Jurassic to lower Cretaceous turbidites; and upper Cretaceous to Pliocene sandstones and shales. The De Long Islands consist of early Paleozoic, middle Paleozoic, Cretaceous, and Neogene sedimentary and igneous (mostly basalt) rocks. These sedimentary, metamorphic, and igneous rocks are mantled by loose Pleistocene and Holocene sediments that range in thickness from a fraction of a meter to about . Digby also noted that some early papers published about the New Siberian Islands incorrectly describe them, often along with other Arctic islands (e.g. Wrangel Island), as being made either up almost entirely of mammoth bones and tusks or of ice, sand, and the bones of mammoths and other extinct megafauna. Some of these papers were written by persons (e.g. D. Gath Whitley) who had never visited the New Siberian Islands and relied upon anecdotes of traders and travelers and local folklore for their descriptions of them, and other articles were written by explorers and ivory hunters untrained in either geology or other sciences. Such statements have been shown to be fictional in nature by detailed studies of the geology of the New Siberian Islands by professional geologists, paleontologists, and other scientists. Ivory deposits As noted by Baron Eduard V. Toll in his account of the New Siberian Islands, sizeable and economically significant accumulations of fossil ivory occur within them. The ivory, along with mammoth and other bones, are found in recent beaches, drainage areas, river terraces and river beds. The New Siberian Islands are unique in the burial and preservation of fossil ivory "in such a wonderful state of preservation that the tusks so found cannot be distinguished from the very best and purest ivory". The abundant bones, even skeletons, of mammoth, rhinoceros, musk-ox, and other megafauna along with the mammoth ivory found in these islands are preserved by permafrost, in which they are encased. The permafrost periodically developed in Late Pleistocene loess, solifluction, pond, and stream sediments as they accumulated. The radiocarbon dating of bones, ivory, and plants, optically stimulated luminescence dating of enclosing sediments, and uranium-thorium dating of associated peats demonstrate that they accumulated over a period of some 200,000 years. Radiocarbon dates obtained from the collagen of 87 mammoth tusks and bones collected from Faddeevsky, Kotelniy, and New Siberia islands ranged from