The percentages of aromatic carbon in several Lower Paleozoic black alum shales of the Baltoscandian, region have been determined by solid state high resolution nuclear magnetic resonance spectroscopy. In marked contrast to the Estonian Middle Ordovician shale kukersite, the black shales have a much higher rank of maturation, and carbon aromaticity in the Cambrian shales exceeds 50 %. The overall structure of the organic matter is similar to that found in typical samples of major US shales.