The Change Islands are underlain by three stratigraphic units of Silurian age. The lowermost unit--the Change Islands Formation (new)--comprises at least 3,000 ft (1,000 m) of alternate thin- to medium-bedded siltite and graywacke with abundant sole marks, convolute bedding, and graded bedding, and several thin beds of oligomictic conglomerate. The Change Islands Formation is overlain conformably by the North End Formation--3,000 ft (1,000 m) of volcanic pyroclastic rocks and lava flows of intermediate composition, including poorly sorted red, green, and purple agglomerate and conglomerate. The upper Change Islands and basal North End Formations contain fossils of early Silurian (Llandoverian) age. In places, the North End volcanic rocks have slumped, in large blocks, int the Change Islands Formation. Thin lenticular bodies of red, volcanically derived sedimentary rock contain mud cracks, ripple marks, raindrop impressions, and flute casts. Overlying the North End volcanic rocks with local erosional unconformity is the South End Formation--at least 2,500 ft (833 m) of well-sorted, cross-stratified, ripple-marked, mud-cracked, gray and green micaceous quartz arenite.

The section conforms with the threefold stratigraphic subdivision of the Silurian Botwood Group recognized by Williams (1964a). Lithologic, stratigraphic, and structural similarities suggest that the threefold stratigraphic subdivision of graywacke, volcanic rocks, and sandstone can be correlated from Port Albert Peninsula to the Little Fogo Islands. The Indian Islands Group may be a time-stratigraphic equivalent of the upper Change Islands and North End Formations.

Paleogeographic restoration indicates that a trough was present northwest of the Change Islands during the late Ordovician-early Silurian, and that a shelf was present on the southeast. Subsequently, the shelf and trough were filled by volcanic debris from rising volcanic islands and later by terrigenous sediments from probable landmasses north-northeast of the Little Fogo Islands and south-southeast of the Indian Islands.