SOIL SURVEY

-28-Throughout much of Yoho National Park there is a ubiquitous shallow (les sthan 50 cm) silty surficial deposit . It is especially evident on stable slopes wher ethere is apparently insufficient mixing or erosion to obliterate the deposit . Similardeposits have been observed in Waterton (Coen and Holland 1976), Banff (King an dBrewster 1976; Walker et al . 1976), Jasper (Wells et at . 1976), Interior Plateau o fBritish Columbia (Sneddon et al . 1972) and other reports of studies throughout theCordillera .The brightly colored Bf horizons generally occur within this surficial deposi twith much paler colors occurring below the till contact . Because of "tree throw" and"frost heaving" causing mixing in the top 20 to 50 cm it is often difficult to identif ythe presence of a silty surficial deposit, but a coarse fragment estimate or weighin gthe 10 cm to 2 mm fraction generally shows a fairly distinct decrease near th esurface . The higher amounts of silt in the surface horizons modifies both profil edevelopment and soil mechanical properties .Layers of volcanic ash have been observed in several locations within Yoh oNational Park . It is suspected that the rather ubiquitous occurrence of this ash ,which has easily weatherable minerals (Beke and Pawluk 1971 ; Pettapiece and Pawluk1972) may contribute to the fairly strong horizon development throughout much of th ePark .