50 Prof. Dr. Pavlow — Oligocene Sandstone in Neocomian Clays. 



about three kilos, from Yavley village a rare stratigraphical pheno- 

 menon — a vein of sedimentary rock which had filled up a Dearly 



vertical fissure in another sedimentary rock, just as we see volcanic 

 veins generally do. 



To distinguish such veins and dikes from volcanic veins and 

 dikes, I shall venture to call these cases by the brief appellation of 

 Neptunic veins or Neptunic dikes. 



The rock forming the Neptunic dike of Alat} T r turned out to bfl 

 a quartz sand mixed with glauconitic grains ; the sandstone found 

 here by the countrymen once formed a dike jutting out towards the 

 ravine, and was only the locally indurated portions of this sand. 

 At the time of my visit all these indurated portions of the dike had 

 been already worked out. The remaining vein of sand, or very 

 friable sandstone, cut a horizontally stratified mass of dark grey 

 and black Neocomian clay, containing some gypsum and occasional 

 beds of fine glauconitic sand with pyritic nodules. The soft clays 

 were well exposed quite up to the vein, and showed no trace of 

 induration. The thickness of the vein varies between 12 and 14 

 inches, its position is nearly vertical or slightly inclined (about 

 10-15 degrees) towards W.S.W., and its strike is about N. 15° W., 

 i.e. nearly parallel to the general direction of the Soura in the 

 neighbouring part of its course. From the direction of the ravine 

 and from the vein being artificially cleared away, it was possible 

 to see the vein exposed at both sides of the ravine. To follow the 

 direction of the vein further across the land was impossible, owing 

 to the superficial drift, as well as to the brushwood and forest of 

 half-grown trees which covered the neighbouring land. Fig. 1 

 represents the vein cropping out at the left side of the ravine, and 

 fig. 2 the same at the right side. The countrymen told us they 

 have found several sandstone veins in this ravine, but when I 

 visited the place, only one was to be seen, the others being probably 

 concealed beneath the landslips and the superficial detritus. 



The sandstone got from the dike occasionally includes small 

 fragments of dark clay detached from the rock forming the walls 

 of the dike, and is rather rich in fossils, well preserved but difficult 

 to get from the hard rock. Shells of Pectunculus predominate 

 among them. 



I have previously defined, in 1892, a small number of species 

 as characteristic of the Lower and partly Middle Oligocene. 1 Since 

 that time our knowledge of the Lower Oligocene Mollusca has 

 been much increased, especially by the publication of the last parts 

 of the important Monograph of Prof. A. von Koenen, 2 and it has 

 been possible for me to verify and rectify my former determinations ; 

 and, moreover, last summer I have had an opportunity of showing 

 the fossils of this sandstone to Prof. A. von. Koenen, and of 



1 Conrptes rendu des travaux du Comite Geolog-ique en 1S92, p. 10. Bull, dtt 

 Coniite Geologique, T. xii. 



2 Das Norddeutsche TJnter-Oligocen unci seiue Mollusken-Fauna, Lief. V, 1898; 

 Lief. VI, 1894. Abh. zur. Geol. Specialkarte v. Preussen unci den Thuringischen 

 Staaten, Bd. X. heft. 5-6. 



