A biosequence of soil profiles, ranging from Black through various stages of Dark Gray to Eluviated Dark Gray Chernozems and a Degraded Brown Wooded soil, is found under a sequence of vegetation ranging from rough fescue prairie (Festuca scabrella association) to encroaching poplar (Populus spp.) and fir trees (Pseudotsuga taxifolia (Poir.) Britt.) in the Porcupine Hills of southwestern Alberta. Samples were gathered to establish the differential physical and chemical changes that have occurred in the soils over an 80-year period.Increased eluviation accompanied a reduction in the percentage of exchangeable calcium but it remained the dominant exchangeable cation in all horizons. Most of the exchange capacity arises from the organic matter. The exchange sites are mainly pH-dependent. The changes in the organic matter, because of the encroachment of trees, are more strikingly evident than are the changes in the mineral matter.Infrared absorption spectra of electrodialyzed humic acids display a conspicuous change in spectral pattern between 2 500 and 1 800 cm−1. There are indications of increased acidity and increased aromaticity in the humic acids of the B horizon as eluviation progresses.