deep borehole core, we tried to determine the mineral composition, origin of the material and the type of sedimentation that took place during the deposition of the analyzed section. To this purpose i prepared 37 core samples. The analyzed samples were taken from a depth of 588 to 711 cm and represent the section with the steep increase in the amount of inorganic material. In order to determine the proportion of loss on ignition the upper half of the samples had to be burned. After that we subjected the ashes, together with the lower half of the samples to X-ray analysis. The results of the Loss on Ignition measurements (figure 1) show that after an initial increase in the amount of organic material, the latter steadily declines with depth until the quantitative dominance of the inorganic component takes place, which is apparent in the last two samples from the depth of 648 and 652 cm. From this we can conclude that the analyzed section of the borehole core represents a transitional phase from inorganic (lacustrine) sedimentation to organic sedimentation, characteristic of a mire. The X-ray diffraction data (figure 2) show that quartz is the most abundant of the minerals present in the samples, the samples also contain clay minerals, micas, plagioclase and carbonates that appear only in the lower half of the analyzed interval. Through the comparison of the mineral composition from the samples with that of the surrounding rock formations i found that most of the inorganic material appears in the nearby environment of the bog, from that we conclude that the bulk of the material originated from the bogs watershed.