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SCIENCE-GOSSIP. 



GEOLOGY 



uml 



CONDUCTED BY EDWARD A. MARTIN, F.G.S. 



To whom all Notes. Articles and material relating to Geology, 



and intended for Science-Gossip, are, in the first instance, to 



be addressed at 69, Bensham Manor Road, Thornton Heath. 



Cheadle Heath Oak. — The huge oak which 

 was recently exhumed during the progress of the 

 Stockport sewage works, cannot in the accepted 

 use of the word be described as a fossil tree. It 

 is interesting, however, as evidence of the com- 

 paratively recent period, in which the rainfall is 

 thought to have been greater than now, and when 

 probably all over the country remains of the 

 immense forests were being imbedded in the debris 

 of the land then forming. It is a huge trunk, and 

 still possesses great boughs, on the surfaces of 

 which is a layer of partially carbonized bark, 

 reminding one of the carbonized bark which covers 

 the "coal-pipes," or standing trees in many a coal- 

 mine. 



Chalk Rock. — As knowledge accumulates in 

 regard to any stratum, zone, or formation, there 

 are never wanting those who, dissatisfied with 

 previous titles, invent new and perhaps more 

 correct designations. Chalk Rock, sometimes called 

 the zone of Holaster planus, has also been called the 

 Reussianum zone from Heteroceras reussianum ; but 

 surely there is no good and sufficient reason why 

 Mr. Wm. Whitaker's old accepted title should not 

 still stand. It is well perhaps to zonate the 

 stratum when tabulating the whole series of zones 

 in the Chalk, but standing alone the Chalk Rock 

 seems to deserve a special name, owing to its being 

 a well-defined horizon, and of hard nodular 

 composition. 



Erosion in the Nile Valley. — Professor Hull 

 has called attention to two great periods of erosion 

 in the Nile Valley, the first of which was during the 

 Miocene period, after the elevation of the Libyan 

 region at the close of Eocene times, and the second 

 during a "pluvial" period extending from late 

 Pliocene times into and including the Pleistocene. 

 The course of the river appears to be through 

 escarpments of the granitic and schistose rocks of 

 Assouan Nubian Sandstone, Cretaceous Lime- 

 stone, and Eocene Limestone. Professor Hull 

 observes that in places, the line of erosion of the 

 primaeval Nile was directed by dislocations of the 

 strata. The unconformity of the Nubian Sand- 

 stone upon the graniies and schists of Assouan is 

 noticeable, and it is apparent that different parts of 

 the Nubian Sandstone are of varying ages. An 

 examination of the terraces of the Nile Valley 

 shows a second line of terraces at a height varying 

 from fifty to a hundred feet above the lower one, 

 which is flooded at the present day. The second 

 terrace is devoid of vegetation, and its deposits 

 have frequently furnished river-shells such as 

 Cyretia fluminalis, Aetheria semilunata, Unio, Paludina, 

 etc. The second terrace is traceable at intervals 

 for a distance of between 600 and 700 miles above 



Cairo. Two old river-channels have also been 

 discovered, one at Koru Ombo, and the other at 

 Assouan itself. Dr. Hull believes the second 

 terrace and the old river-valleys to be due to the 

 former greater volume of the river, and not to 

 subsequent erosion of the valley. He gives evi- 

 dence of the existence of meteorological conditions 

 sufficient to give rise to a "pluvial" period, 

 following in this respect other authors who have 

 also considered that the volume of the Nile has 

 been greater in former times. 



Phosphatic Chalk. — The phosphatic chalk 

 described by Mr. A. Strahan from the horizon 

 of the Chalk Rock at 'Lewes resembles in composi- 

 tion and microscopic character a similar deposit 

 found at Taplow. At the latter place, however, it 

 occurred at the top of the Upper Chalk, whereas 

 the Lewes deposit, of course, occurs at the base of 

 the Upper Chalk. At both places it consisted of 

 brown phosphatic grains contained in a white, 

 chalky matrix, which also included numerous 

 pellets attributed to small fish, phosphatized 

 foraminifera, chips of bone and fish teeth. It 

 rested upon a hard, nodular chalk with white chalk 

 beneath, traversed by branching pipes of the brown 

 variety. These floors are thought to be associated 

 with pauses or changes during the period of 

 sedimentation. 



Formation of Boulder Clay. — Dr. Croll was 

 evidently a strong believer in the formation of 

 boulder clay by land-ice. Submergence had, in 

 his opinion, but a small part in its formation. 

 Opinions are still, however, very divided amongst 

 glacialists. Dr. Croll says: "It is physically 

 impossible that any deposit formed by icebergs 

 could be wholly unstratified. Suppose a mass of 

 the materials which would form boulder clay is 

 dropped into the sea from, say, an iceberg, the 

 heavier part, such as stones, will reach the bottom 

 first. Then will follow lighter materials, such as 

 sand, then clay, and last of all the mud will settle 

 down in fine layers. Unstratified boulder clay. . . . 

 must be the production of land-ice. . . . The 

 notion that unstratified boulder clay could be 

 formed by deposits from floating ice is not only 

 erroneous, but positively pernicious." 



British Jurassic Brachiopoda. — We have 

 received Part ii. of Mr. J. W. D. Marshall's 

 " Notes on the British Jurassic Brachiopoda," 

 reprinted from the " Proceedings of the British 

 Naturalists' Society." Mr. Marshall points out 

 the changes in classification which have been 

 rendered necessary since 1SS4, the date of the 

 publication of Dr. Davidson's "General Summary 

 to the Brachiopoda," and the date of that great 

 brachiopodist's death. Terebratitla proper is first 

 met with in Jurassic rocks, although Dielasma, a 

 near ally, is found in Devonian, Carboniferous 

 and Permian rocks. Eight to ten species of an 

 allied genus Liothyrina, are found in existing seas. 

 We note a useful feature in the etymology given of 

 each genus described. The reasons are given for 

 the founding in 1850 of the genus Waldheimia, 

 King, which includes many forms hitherto classed 

 as Terebratitla. The author summarises in tabular 

 form the approximate number of British Jurassic 

 Brachiopoda, and finds that there are 241 species, 

 fifteen doubtful species, and forty-four varieties. 

 Of these, Rhyncomella, Terebratitla and Waldheimia, 

 show [no less than eight-seven per cent, of the 

 whole. 



