In the rocks exposed on a low mountain ridge near the village of Świny, two different episodes of the geological development of the Kaczawskie Mountains are recorded.
Two different types of rocks
The rocks located at the foot and in the lower part of the slope are composed of clastic, coarse-grained sedimentary rocks called conglomerates. The rock fragments that make up these conglomerates originated from the rapid erosion of a newly uplifted mountain massif. In the higher parts of the slopes and on the ridge itself, there are outcrops of rocks composed of material with a distinctly different character. This is a rock of pink to reddish color, within which only a few mineral components are visible to the naked eye. White, creamy, or pinkish, often rectangular and up to 1 cm in size, is feldspar. Gray, transparent, rounded in outline, and slightly smaller in size than feldspar is quartz. Black biotite sheets are less common. It is a rhyolite rock, which is an igneous extrusive rock.
Porphyritic texture and rock fractures
The term “porphyry” or “quartz porphyry” is often used to refer to rocks with such appearance. Porphyries are volcanic rocks in which only individual crystals are visible to the naked eye embedded in a cryptocrystalline mass. Such a type of rock structure is called porphyritic structure. Carefully observing these rocks, you will notice the arrangement of visible feldspar crystals. It is the result of the directional alignment of crystals during the flow of lava. Most bodies, as they cool down, reduce their volume, and the same is true for lava. The reduction in volume creates stress within the rock, leading to the formation of cracks. These cracks are not chaotic but form three distinct systems that are mutually perpendicular to each other. The first of these systems, which dip at small angles (10-20°) towards the southeast, is parallel to the alignment in the rock defined by the feldspar. These fractures are the so-called bedding joint. The other two systems of fractures visible in these rocks are nearly vertical and oriented perpendicular to each other. These systems of fractures are collectively referred to as thermal joints.
Where did the rhyolites in Świny come from?
Rhyolites from the Świny area were formed as a result of the solidification of a lava flow or they are strongly compacted rhyolitic tuffs, also known as ignimbrites, deposited by a pyroclastic flow. They form a cover that can reach a thickness of up to 100 metres and extends in this region from Kwietnik to the vicinity of Wolbromek. The age of these rocks is estimated to be around 290 million years, that is the early Permian period. The Permian period and the preceding geological period known as the Carboniferous were characterized by intense volcanic activity in the region of what is now Lower Silesia. It is estimated that during the Carboniferous and Permian periods, over a span of approximately 50 million years, several thousand cubic kilometers of igneous rocks, both intrusive (such as the granites of the Karkonosze Mountains, Strzelin area, or Strzegom area) and extrusive, were added to the geological inventory of this region.
Dead stream
The mountain ridge on which the castle is located, and where the highest point of the ridge is at 369 metres above sea level, is undercut by the valley of the “dead” stream from the southwest. The “dead” stream is one that flowed through here in the distant geological past. Because of this, the ridge stands out in the landscape compared to the surrounding terrain. From the northwest side, it gently slopes down towards the plateau that extends towards Jawor. The isolated rocks visible on the slopes of the hill are denudation remnants, which are the remains of the weathering of a larger rock massif.
