Szabó János szerk.: Fragmenta Mineralogica Et Palaentologica 19. 2001. (Budapest, 2001)

young barnacles to hydroids and bryozoans. Algae are removed from rocky surfaces by the rasping action of the radula. Polyplacophorans range in size from only a few mm long to some 10 cm. They are an ancient group, isolated valves having been found in the Upper Cambrian, but the fossil record is generally poor. At present there are some 10 families and about 750 living species in the seas. Locality Figure 1 — Sketch map showing the location of borehole Szokolya-2. Hungary and the Carpathian Basin belonged to the Central Paratethys during the Miocene period, therefore a significant part of the basin contains marine Miocene formations. The Börzsöny Mountains are situated at the northern border of Hungary, at the westernmost part of the so-called Inner Carpathian Neogene to Pleistocene calc-alkaline Volcanic Chain. The basement consists of carbonate rocks related to the Transdanubian Central Range to the south and crystalline schists of the Veporides to the north, separated by the Diósjenő line. These formations are overlain mostiy by Oligocène and Lower Miocene sedimentary rocks. The main mass of the mountains consists of andesitic-dacitic volcanic rocks, which are 1000 m thick at some places. According to BÁLDI & KÓKAY (1970) the volcanic formations developed in the Early Badenian during a relatively short time. Recendy, KARÁTSON et al. (2000) summarized the volcanic evolution of the Börzsöny Mts and they postulated a longer interval than BÁLDI & KÓKAY (1970) for the volcanic activity. The volcanic rocks are overlain by early Badenian Leitha Limestone and some other sedimentary rocks, including the examined sandy marls and marly sandstones at Szokolya. These sedimentary formations are situated mainly along the western and southern margin of the mountains. Several drillings were made in the examined area during the geological mapping of the Börzsöny Mts in the years around 1970. The borehole Szokolya-2 was made in 1971 (Figure 1). The simplified sequence of the borehole is the following (all formations are Badenian in age) (Figure 2): Figure 2 — Simplified sequence of borehole Szokolya-2 (modofied after BOHN-HAVAS 1972). 1 - soil and scree; 2 limestone; 3 — sand, sandstone; 4 — marl; 5 - clay; 6 — andésite; 7 — location of Polyplacophora valves. 0—2.8 m: soil and scree 2.8—5.4 m: yellowish grey limestone, sandy limestone 5.4—9.6 m: yellowish grey calcareous sandstone 9.6—16.5 m: yellowish grey sandy marl 16.5—38.3 m: yellowish grey sandstone 38.3—76.7 m: grey sandy marl