GEOLOGICAL STRUCTURE AND CAMBRIAN ROCKS 



The geological structure of Bennett Island was briefly characterized by v. Toll in his 

 journal, found together with his collections. Von Toll's account runs as follows: 



ccDie Bennett-Insel ist, wie die topographische Aufnahme F. Seebergs ergibt, nicht 

 grosser als 200 Quadratkilometer. Die grosste Hohe der Bennett-Insel iibersteigt nicht 

 1500 Fuss. Ihrem geologischen Baue nach erscheint sie als Fortsetzung des mittel- 

 sibirischen Tafellandes. Sie ist namlich aus kambrischen Schiefern aufgebaut, die von 

 Basalten durchsetzt und iiberdeckt werden.^ An einigen Stellen sind unter den Basalten 

 Braunkohlenfloze gelagert, im Zusammenhang mit welchen Baumreste (Koniferen ?) erhalten 

 -sind»(v. Toll, 1909, p. 591). 



The Cambrian rocks of which samples are present are made up exclusively of a rather 

 coarse and hard, black or dark grey, arenaceous clay shale, sometimes containing calcareous 

 nodules or thin seams. Slides of the rocks have been examined by Dr. N. H. Magnusson, 

 of the Swedish Geological Survey, who has kindly given the following account of the petro- 

 graphical character of the rocks : 



(cThe shale has a matrix mainly composed of chlorite and muscovite, in which frag- 

 ments of quartz are fairly abundant and scattered laminae of graphite and rare grains 

 of sulphides are to be seen. In the nodules calcareous matter is fairly abundant; it contains 

 quartz fragments, often accumulated into thin layers, scales of chlorite and muscovite. 

 Coarser calcite crystals form various sized accumulations. The rocks suggest that they have 

 been to some extent subject to metamorphosis». 



In part of the shale, fossils are frequent, but usually poorly preserved as casts or 

 imprints. The fauna has been incidentally mentioned in the literature. Tims, before tlie 

 collection first brought home was sent to Holm, it was cursorily looked over by Fr. Schmidt, 

 who recognized the Scandinavian species Anomocare excavatum (Ang.) besides indistinct 

 Ostracoda (?).^ In 1924 Professor 0. Holtedahl gave the following particulars of the fauna 



1 Not only Cambrian but also Lower Ordovician 

 deposits build up the island, since black shales containing 

 Didymograptus, Tetrui/raptus and Phtjllogrnptus are to 

 be found in v. Toll's collections too. The Ordovician fauna 

 will be described by Dr. G. T. Troedsson. 



2 Centralblatt fur Min., Geol. und Palaeont., 1904, 

 p. 527. As no Ostracoda or similar forms are to be seen 

 in the shale, the latter statement is supposed to refer to 

 very small indistinct Acjnosiidae, which are fairly common 

 in some slabs, 



