ART. XIII.-On the Occurrence of Structures like Walcott's Algonkian Alge in the Permian of England; by OLAF HOLTEDAHL.

During his studies on the Paleozoic rocks of Finmarken and Bear Island, the writer became acquainted with the peculiar organism-like structures in dolomites and limestone which American paleontologists have generally referred to Cryptozoon. In a summary of my stratigraphical results in Finmarken published in this Journal in 1919,' the opinion was stated that the Cryptozoon "species," such as Gymnosolen ramsayi described

by Steinmann from northern Russia, can not be regarded as real fossils which deserve generic and specific names, but rather that this type of sedimentary rock must be considered to represent "a chemical precipitation, one, however, that probably came into existence through the organic processes of living organisms." Accordingly, as a general term for these structures, which appear to be genetically related to oolites, it was proposed that we should use Kalkowsky's name stromatolites.

As to the kind of organisms which may have played a part in the process by which the stromatolite lamina were precipitated, I mentioned, among others, the cells of bluegreen algæ described by Walcott from Camasia spongiosa 1 Vol. 47, p. 96.

in his widely known paper on the "Pre-Cambrian Algonkian algal flora."" Besides the species of Collenia, which certainly also represent only variations of the stromatolite structure, Walcott described a great number of "species" of algae whose beautiful structure and great geologic age have caused no little sensation among geologists. From the Newland limestone of the Belt series are described no fewer than six new genera, Newlandia,

cott.

Camasia, Weedia, Kinneyia, Greysonia, Copperia, the first mentioned with four, the rest with only one species.

Recently I happened to see several of these types of structures in the Permian limestones of England and should like to draw the attention of American geologists to their occurrence. During a very short stay in Newcastle-upon-Tyne in June 1920, my friend Leonard Hawkes, of Armstrong College, who knew of my interest in these peculiar sedimentary structures, arranged an excursion to the Permian magnesian limestone of the Durham district in order to have me see its so-called 2 C. D. Walcott, Smithson. Misc. Coll., 64, No. 2, 1914.

concretionary limestones. I was fortunate in having as a guide Doctor D. Woolacott, who has studied the district in great detail and published several important papers on its stratigraphy and tectonics. We visited especially the extensive Fulwell quarries, where the concretionary structures are seen in wonderful variation. Here there are concretions of the more ordinary sort, e. g., the "cannon ball" and the "botryoidal" types, along with a great display of other more cellular structures, and

among these I recognized at once several types which struck me as being identical with those shown by Walcott in the splendid illustrations accompanying the paper cited.

The many curious structures of these Permian limestones were described in 1835 by Sedgwick, whose very detailed and accurate descriptions give a clear account of the great variety of these stromatolite structures in the Permian limestone of eastern England. His illustrations, A. Sedgwick, Trans. Geol. Soc., London, 2d ser., 3, 37-124.

on the other hand, give no very distinct idea of their character. In 1891, Garwood published a paper entitled "On the origin and mode of formation of the concretions in the magnesian limestones of Durham," treating, however, mainly concretions of the more ordinary types, some of which are depicted. In the British Association report for 1900, Abbott has an abstract of a paper on these concretionary types, and two years later another very short abstract. Trechmann in 1914 writes on "The lithology and composition of Durham magnesian limestones" and in an earlier paper has remarks on the concretionary structures. Other very important contributions are Woolacott's papers of 1912 and 1919.7

FIG. 4.-Four-fifths nat. size. Compare with Greysonia basaltica Walcott.

The purpose of the present article is not to give a detailed description of the Durham concretions, since such may be found in the papers above mentioned, and since a full description with necessary illustrations will, it is to be hoped, soon appear from the English investigators, but rather to draw attention to the resemblance of some of these Permian concretionary structures to those of the Algonkian Newland limestone, and to illustrate this likeness by photographs of specimens which were collected during the excursion and kindly sent to Kristiania by Mr. Hawkes.

E. J. Garwood, Geol. Mag., dec. 3, vol. 8, 434-440.

G. Abbott, Rept. British Assoc. Adv. Sci., for 1900, pp. 737-739; Quart. Jour. Geol. Soc., London, 59, 51, 1903.

C. T. Trechmann, Quart. Jour. Geol. Soc., London, 70, 232-265, 1914; Ibid., 69, 184-218, 1913.

D. Woolacott, Proc. Univ. Durham Phil. Soc., 4, 241, 1912; Geol. Mag., dec. 6, 6, 452, 1919.

Structure of the Newlandia type.-Walcott's diagnosis of Newlandia is (p. 104): "More or less irregular semispherical or frondlike forms built up of concentric, subparallel, subequidistant thin layers that may be connected by very irregular, broken partitions." By comparing my figure 1 with Walcott's plate 6, especially figure 2 (of N. frondosa), the strikingly similar features will be seen. This likeness is still greater between my figure 2 and Walcott's plate 7, figures 1 and 2, where the

concentric laminæ are less strongly and less regularly curved. My figure 3 shows a structure similar to his figure 1 of the same plate, yet with somewhat thinner and regularly spherical laminæ. A small ball-like specimen in my collection, 6 cm. in diameter, shows a concentric structure with the same very slight thickness of the laminæ as in Walcott's illustrations of N. lamellosa, plate 10, figures 1 and 2. There is no doubt that the same structure can easily be found in larger masses, giving a picture like those of Walcott.

Structure of the Greysonia type.-Walcott's diagnosis of Greysonia (p. 108) reads as follows: "Irregular, cylindrical or tubular growth with relatively thin walls except at the union of three or more tubes, where the walls are thickened ... The tubes are large, irregularly rhomboidal or pentagonal in section with the interior now filled in with a dark bluish-grey limestone. The walls