Szekessy Vilmos (szerk.): A Magyar Természettudományi Múzeum évkönyve 57. (Budapest 1965)

Csalogovits, I. J.: Geological and petrological conditions of the Szanda - Bercel area

tectonic character of tertiary volcanism, showing a passive slip-filling character and effusing from the slips — referred to by B. BALKAY — can be proved in this area too. Regarding the Cserhát range as a whole, the radial structure starting from the Mátra mass is characteristic of the development of dike trends. This is indicative partly of a close relationship with the volcanism of the Mátra range, partly of the synorogenic character of tectonism here. The structural trends that developed after the consolidation of the magma follow the main NNE — SSW structural trends which are nearly perpendicular to the dike trends. But the development of these slips took place before, or simultaneously with, the postmagmatic phenomena that followed volcanism immediately: namely the trends of the hydrothermal dikes are identical with these, and post-magmatic effusion took place already in crushed zones connected with these structures. Only horizontal shifts took place along the slips: this is evidenced by horizontally displaced parts of dikes (Istenhegy, Pereshegy. Pisköhegy, etc.). No vertical shifts can be demonstrated in the volcanic covers (Mt. Bercel) although these are cut by slips as well. Following this, a vertical shift of large extent took place along the former structucal lines of the NNE — SSW trend : this can be concluded from the main structural line running in the direction of Bér — Herencsény along which the volcanic covers, characteristic of the western part of Cserhát, faulted to a lower level and thus were spared erosion, while the vulcanite groups remaining at a higher level in the western part were denuded by erosion, down to the openings of effusion of dikes and slip volcanoes (Bercel-Szanda). The tectonically intact position of the Pleistocene sediments indicates a subsequent consolidation of the area. Volcanological and petrological investigation of pyroxene-andesite volcanism A) Forms of volcanic deposition and phenomena of cooling Of the deposition forms of volcanic formations, the aforesaid nearly vertical dikes, slip volcanoes produced by the widening of these dikes, uneroded wrecks of cover occasionally occuring above them, and covers can be found in this area, as can be concluded from the tectonic conditions of the area, the deposition of dikes is only a secondarily developed form that indicates a higher degree of erosion. An analysis of the forms of cooling is especially justified by the bight degree of erosion. The columnar jointing character and lineation developed on the original forms of deposition, and a statistical analysis of the partings of cooling indicates also the amount and form of original rock masses before erosion. It appears that if columnar jointing forms emerge on the covers, the vertical angular deflection of the colums — if related to an axis that is adopted from the effusion opening of intact covers — is of a symmetrical structure if compared to the openings, and that the angle of inclination becomes greated as the distance from the opening grows. The cause of this phenomenon must be sought in the convex shape of the surface of the viscous lava that flowed onto the top since the columns were formed vertically to the isotherms that developed parallel with the surface, the changes in surface incline are greatest at the edges and this means also a change in the angle of inclination of the columns. A statistical analysis of the columnar jointing trends indicates that — contras-