The Hogland Series are a

series Series may refer to: People with the name * Caroline Series (born 1951), English mathematician, daughter of George Series * George Series (1920–1995), English physicist Arts, entertainment, and media Music * Series, the ordered sets used in ...

of Subjotnian sedimentary rocks exposed in the island of

Gogland Gogland or Hogland (russian: Гогланд, transliteration from original sv, Hogland; fi, Suursaari) is an island in the Gulf of Finland in the eastern Baltic Sea, about 180 km west from Saint Petersburg and 35 km from the coas ...

( sv, Hogland), the Sommer Islands and the nearby sea bottom in the

Gulf of Finland The Gulf of Finland ( fi, Suomenlahti; et, Soome laht; rus, Фи́нский зали́в, r=Finskiy zaliv, p=ˈfʲinskʲɪj zɐˈlʲif; sv, Finska viken) is the easternmost arm of the Baltic Sea. It extends between Finland to the north and E ...

. The series encompass

quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical form ...

-rich conglomerates and

breccia Breccia () is a rock composed of large angular broken fragments of minerals or rocks cemented together by a fine-grained matrix. The word has its origins in the Italian language, in which it means "rubble". A breccia may have a variety of di ...

s plus some volcanic rocks of

mafic A mafic mineral or rock is a silicate mineral or igneous rock rich in magnesium and iron. Most mafic minerals are dark in color, and common rock-forming mafic minerals include olivine, pyroxene, amphibole, and biotite. Common mafic rocks include ...

composition in the form of

lava flow Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or und ...

s and some more silica-rich igneous rocks including

quartz-porphyry Quartz-porphyry, in layman's terms, is a type of volcanic (igneous) rock containing large porphyritic crystals of quartz. These rocks are classified as ''hemi-crystalline acid rocks''. Structure The quartz crystals exist in a fine-grained matrix ...

. The porphyries, which lie at the top the pile, share their origin with the

rapakivi granite Rapakivi granite is a hornblende-biotite granite containing large round crystals of orthoclase each with a rim of oligoclase (a variety of plagioclase). The name has come to be used most frequently as a textural term where it implies plagioclase r ...

s found nearby. An exhumed Subjotnian

erosion surface In geology and geomorphology, an erosion surface is a surface of rock or regolith that was formed by erosion and not by construction (e.g. lava flows, sediment deposition) nor fault displacement. Erosional surfaces within the stratigraphic reco ...

is exposed on the island.

References

{{russia-stub Geology of European Russia Mesoproterozoic Stratigraphy of Europe