The bottom deposits from parts of five lakes in central and northern Minnesota have been studied and their depositional histories interpreted. Four of the lakes, Minnetonka, Prior, Johanna, and Cedar, although very different from each other in limnologic detail are all eutrophic (organically productive) carbonate-hardness lakes in which the bottom deposits are mainly organic brown and gray coprogenic ooze, copropel, or "gyttja." These lake basins are located in glacial drift. The fifth lake, Burntside, located in Precambrian bedrock, is a soft-water oligotrophic lake (low organic productivity) in which the bottom deposits are principally silt.

The constitution, properties, and facies of the lake sediments are discussed. Internal standing waves are believed to have been important in the distribution of the copropelic sediment.

Lipoid extracts of some of the sediments were obtained with a benzene-methanol-acetone mixture and were separated by adsorption chromatography. Fractions representing saturated and aromatic hydrocarbons were found in all the extracts. Partial characterizations were made by means of absorption spectra in the visible, infra-red, and ultra-violet ranges. In Burntside the extracts were mainly hydrocarbons plus some asphaltenes, but with very little polar organic substance. The other lakes yielded greater proportions of these polar substances, probably as a result of their heavy crops of protein-rich blue-green algae and pondweeds which are mainly lacking in oligotrophic Burntside Lake. The largest quantity of hydrocarbons (0.36% of sample) was obtained from the copropel of Cedar Lake in w ich the saturated and aromatic fractions were about equally represented.