The petrography of the Snochowice Beds (Lower Jurassic, western Mesozoic margin of the Holy Cross Mountains)

The Snochowice Beds – the Lower Jurassic gravels and conglomerates – are composed of the fragments of the most resistant rocks: the vein quartz, quartzites, quartzite sandstones and conglomerates, lydites and jaspers. The results of performed investigations allowed to modification of the existing opinion about the source areas. The results of petrographical analysis also allow to compare the group of the Snochowice Beds pebbles to the pebbles of the Lower and Upper Triassic rocks from the Mesozoic margin of the Holy Cross Mountains and the Inner Carpathians. The similarity of the main components: the pebbles of quartzites, lydites and jaspers of the Carpathian Triassic rocks and the Lower Jurassic gravels was the basis to identifying the Bohemian Massif as the source area, which was build mainly of the Paleozoic metamorphic and sedimentary rocks. In the Snochowice Beds pebbles were recognized also parts of rocks similar to the Cambrian rocks underlying the Jurassic rocks on the Upper Silesia Block