One of the more characteristic hills in the Płakowice Uplands (a part of the Kaczawskie Mountains) is the mound of Kopka (343 metres above sea level). It is a denudation inselberg towering over the village of Czaple. In many places on this hill, you can find traces of obtaining quarried sandstone, from which it is constructed. On the walls of smaller or larger quarries, beds, or layers, are clearly visible. These are layers or sets of layers with similar characteristics, separated from the rocks lying below and above them by parallel boundary surfaces. The deposits in a single bed are a record of a geological process that was in some way different from the process that shaped the rocks lying below and above. They could be differences, for example, in the strength of flowing water, the size and type of transported material, or the direction from which this material was transported. Within the beds, layers may be visible, and their characteristics such as geometry and grain features allow geologists to recognize whether a particular deposit was deposited in a terrestrial or marine environment. In such considerations, organic fossils are also helpful, as the type of organisms found unequivocally links a given deposit to the environment in which these organisms lived.
In the quarries on the hill Kopka, the beds have a thickness ranging from 1 m to 4 m and are inclined at slight angles (approximately 10°) towards the northeast. Within them, cross-stratification is visible. The sandstones from this location contain few fossils; however, fossils such as starfish, sea urchins, and shark teeth have been described. Much more common are so-called trace fossils, i.e., traces of the activity of living organisms, such as burrows or tracks. The types of fossils found here unequivocally indicate that this sediment was formed in a marine environment, relatively shallow and well-illuminated. The cross-stratification visible here is a record of the movement on the seafloor of forms resembling eolian dunes, called ripple marks (smaller) or sand waves (larger), depending on their size. The characteristics of these forms indicate that they were formed as a result of the action of coastal ocean currents driven by wind activity. These deposits are the result of the flooding of the area of present-day Lower Silesia (and all of Poland) during the Upper Cretaceous period by the waters of a shallow, inland sea. It is believed that these rocks were formed during the Upper Cretaceous period, around 86-90 million years ago.
The primary component of these sandstones is quartz, which can constitute almost three-quarters of the total rock volume, with a few percent being feldspar, and the rest being the matrix binding these components, i.e., the cement. This cement is generally formed from clay minerals, with variable content of iron oxides and hydroxides, resulting in color changes from creamy to yellow or beige.
One striking feature in the outcrops of these rocks is the widespread occurrence and regularity of mutually perpendicular fractures cutting through the sandstones – these are known as joint fractures. Thanks to the presence of these fractures, it was easy to extract large and regular blocks of rock, which have been used in construction for centuries. The sandstones from the Czaple area were used in the construction of well-known structures such as Grodziec Castle, the stock exchange building on Solny Square in Wrocław, the Grand Theatre in Poznań, the southern facade of the cathedral in Berlin, and the Reichstag building.
