felix-femina) large-leaved sandwort (Moehringia macrophylla) leafy lichen (Peltigera spp.) low spike-moss (Selaginella selaginoides) moonwort grape-fern (Botrychium lunnaria) mountain avens/yellow dryas (Dryas drummondii) mountain bladder fern (Cystopteris montana) mountain cranberry (Vaccinium vitis-idaea) mountain clubmoss (Huperzia selago) mountain fir-moss (Huperzia appalachiana) northern meadow sedge (Carex praticola) northern white anemone (Anemone parviflora) old man’s beard (Usnea spp.) prairie spikemoss (Selaginella densa) prickly rose (Rosa acicularis) rand's goldenrod (Solidago simplex ssp. randii) red stemmed feather moss (Pleurozium schreberi) reindeer lichen (Cladonia rangiferina) rock tripe (Umbilicaria spp.) rose twisted stalk (Roseus streptosus) roundleaf shadbush (Amelanchier sanguinea) scirpus sedge (Carex scirpus) smooth woodsia (Woodsia glabella) sphagnum moss (Sphagnum spp.) spike trisetum (Trisetum spicatum) stair-step moss (Hylocomium splendens) viviparous knotweed (Polygonum viviparum) white mountain-saxifrage (Saxifraga paniculata) wild chives (Allium schoenoprasum var. sibiricum) wild sarsaparilla (Aralia nudicaulis) Geology The islands are not made of slate; the rock is mainly of metamorphosed volcanic rocks greater than 2.7 billion years old. Also present are sedimentary rocks of the Rove and Gunflint formations, approximately 1.85-2.10 billion years old. There is evidence that about 1.1 billion years ago, there was volcanic centre on Paterson Island, however almost all volcanic rocks have been removed by erosion. The youngest rocks are diatremes, referring to breccia-filled volcanic pipes that were formed by gaseous explosions. They occur as dikes or sills which criss-cross the all older rocks types. Also located in the islands are good examples of shatter cones, rare geological features formed in bedrock by the high velocity shock waves created by meteorite impacts. They have a distinctively conical shape with thin grooves (striae) that radiate from the top (apex) of the cone. The Slate Islands are home to a shatter cone measuring , one of the largest examples in the world (pictured here). Allogenic breccia is present, notably on the east and north sides of the islands. Impact crater The Slate Islands mark the centre of a large meteorite impact crater. The original crater rim is estimated at about in diameter, but this and most of the crater has subsequently eroded away, leaving the islands which are interpreted as a central uplift. The age of the impact event is estimated to be about 450 million years (Ordovician). Another source estimates the age at 800-500 million years (late Proterozoic to early Paleozoic). It may be one of several Middle Ordovician meteors that fell roughly simultaneously 469 million years ago, part of a proposed Ordovician meteor