the German word Steinöhl (meaning: stone oil), which was used by Hupel but which most likely did not mean oil shale in the context of his publication. In the second half of the 18th century, the St. Petersburg Free Economic Society started to search for information about combustible minerals which as fuels would replace the decreasing stock of trees in the European part of Russia. As a result of these inquiries, the Society received information about a combustible mineral found at the Kohala Manor near Rakvere. According to the landlord of the Kohala estate, Baron Fabian Reinhold Ungern-Sternberg, the 'burning rock' was discovered at a depth of about ten meters when a spring was opened on the slope of a sandy hump, as it was during the digging of a well some years earlier on the same slope. This discovery was briefly mentioned in a paper prepared by the German chemist Johann Gottlieb Georgi and presented by the Actual State Councillor Anton-Johann Engelhardt at the meeting of the Society in 1789. The first scientific research into the rock's oil yield, using samples from the Vanamõisa village of the Kohala Manor, was published by Georgi at the Russian Academy of Sciences in 1791. In 1838 and 1839, the Baltic German geologist Gregor von Helmersen published a detailed description of the deposits of kukersite in Vanamõisa and graptolitic argillite in Keila-Joa. In 1838 he made a thorough experiment to distil oil from the Vanamõisa oil shale deposit. During the 1850s, large-scale works were undertaken in Estonia to transform excessively wet land into land suitable for agriculture; this included the digging of drainage ditches. In the process, previously unknown layers of oil shale were discovered in several locations. In the years 1850–1857, the territory of Estonia was explored by the Baltic German geologist Carl Friedrich Schmidt who studied these findings of oil shale. Russian chemist Aleksandr Shamarin, who at the end of the 1860s had studied the composition and properties of oil shale originating from the Kukruse area, concluded it made sense to use oil shale for the production of gas and as a solid fuel. However, he considered shale oil production unprofitable. During the remainder of the 19th century oil shale was used locally as a low-grade fuel only. For example, in the 1870s, Robert von Toll, landlord of the Kukruse Manor, started to use oil shale as a fuel for the