Geological mapping in the Espanola-Willisville area has established a stratigraphic succession similar to that of the Huronian of the Bruce Mines-Blind River area. Seven lithologic units are recognized, as follows is ascending order: Mississagi, Bruce, Espanola, Serpent, Gowganda, Lorrain formations and Banded Chert-like Siltstone. The Huronian strata are largely arenaceous rocks; mainly feldspathic sandstone and conglomeratic muddy sandstone (tillite?).

A wide variety of sedimentary structure has been recognized. Cross-bedding and dimensional fabric of embedded clasts were used in a paleocurrent study. Cross-bedding azimuth measurements were taken from the Mississagi, Espanola, Serpent and Lorrain formations. The general direction of sediment transport throughout the Huronian of the Espanola-Willisville area was from the north-northwest and north-east quadrant. Dimensional fabric study of the Bruce and Gowganda conglomeratic deposits reveals a similar "line" of sediment transport.

Size analyses are based on measurements in thin-section. Inman's (1952) and Folk and Ward's (1957) size parameters were computed wherever possible. Modal analyses were carried out on the arenaceous and conglomeratic rocks. Rocks of the arenaceous units (Mississagi, Espanola, Serpent, mixed zone of the Gowganda and Lorrain) are predominantly poorly to moderately well sorted, muddy medium-grained sandstones. The grain size distribution of most samples is unimodal. Rounded pebbles are rare in the Mississagi and Serpent formations but more common in the Lorrain Formation. Sand size detrital grains are generally subrounded and seldom rounded to well rounded. Compositionally, these rocks are mostly submature or immature subarkose and arkose (Mississagi, Serpent and Lorrain). However some of the rocks (Espanola) are calcareous. The upper part of the Lorrain consists of mature to supermature quartzarenite. Typically the Bruce and Gowganda conglomeratic deposits are poorly sorted pebbly conglomeratic muddy sandstones: immature subarkosic lithic wacke. Grain size distribution of the fine-clastic aggregate generally shows a principal mode in the fine sand grade and a poorly marked submaximum in the gravel fraction (4-8mm).

The source area for the Huronian strata consisted largely of granitoid rocks. Archaean volcanic and immature metasedimentary rocks provided a secondary source.

The uniform distribution of cross-bedding azimuths in all the Huronian formations, from Mississagi through Lorrain, is similar to that of known ancient and modern fluvial (coastal plain) deposits. The variance at the formation level is usually less than 4,000. Overall lack of textural and compositional maturity and occasional presence of unstable sedimentary and metamorphic rock fragments suggest that much of the Mississagi sediment was deposited in an environment where wave or current potency was low and reworking minimal.

The conglomeratic muddy sandstones of the Bruce Formation are in many respects similar to the Gowganda conglomeratic deposits and may have been deposited under glacial conditions. Much of the Espanola and Serpent formations was deposited in an environment similar to that of the Mississagi. The lower and upper conglomeratic units of the Gowganda Formation are considered to be glacial in origin. The intervening laminated and massive argillite was deposited during an interstadial or interglacial period; and the uppermost mixed unit of the Gowganda Formation possibly represents a post-glacial outwash(?) deposit.

The sedimentary history of the overlying Lorrain was marked by tectonic instability resulting in the deposition of immature arkosic wacke. Gradual attainment of tectonic stability and protracted weathering of the source area resulted in the deposition of progressively more mature sediment. The well-washed supermature quartzarenite occuring near the top of the Lorrain Formation was possibly deposited in a migrating shore zone environment. The banded chert-like siltstone, the uppermost member of the Huronian succession of the Espanola-Willisville area, consists of very fine-grained terrigenous detritus winnowed from the turbulent shore zone.

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