MAP UNITS FOR THE GENERALIZED GEOLOGIC MAP OF THE UNITED STATES, PUERTO RICO, AND THE U.S. VIRGIN ISLANDS, 2005 PLUTONIC ROCKS SEDIMENTARY ROCKS (Suffix "g" indicates granitic rocks; "i," intermediate rocks; (Includes mixed sedimentary and volcanic rocks) "m," mafic rocks; "u," ultramafic rocks; "a," anorthosite) Q Quaternary Tg Tertiary nT Neogene nTg Neogene pgT Paleogene pgTg KT Cretaceous and Tertiary pgTi Paleogene K Cretaceous pgTm c Mesozoic KTg Cretaceous and Tertiary lc Lower Mesozoic (Triassic and Jurassic) Kg Cretaceous gc Paleozoic and Mesozoic cg Mesozoic g Paleozoic lcg ug Upper Paleozoic (Pennsylvanian and Permian) lcm Lower Mesozoic mg Middle Paleozoic (Silurian, Devonian, and Mississippian) lcu lg Lower Paleozoic (Cambrian and Ordovician) gcm Paleozoic and Mesozoic Zg Late Proterozoic and lower Paleozoic ugg Upper Paleozoic a Proterozoic mgg Middle Paleozoic Z Late Proterozoic mgm Y Middle Proterozoic gg Paleozoic X Early Proterozo lgg Lower Paleozoic A Archean Zgg Late Proterozoic and lower Paleozoic Zgm ag Proterozoic Zg Late Proterozoic VOLCANIC ROCKS Yg Qv Quaternary Ym Middle Proterozoic Tv Tertiary Ya nTv Neogene Xg Early Proterozoic TQv Tertiary and Quaternary Xm pgTv Paleogene Ag Archean KTv Cretaceous and Tertiary u Age uncertain cv Mesozoic Kv Cretaceous METAMORPHIC ROCKS l cv Lower Mesozoic (Triassic and Jurassic) (Suffix "n" indicates gneisses and associated rocks) gcv Paleozoic and Mesozoic Phanerozoic (amphibolite facies) gv Middle Paleozoic Phanerozoic (blueschist facies) gv Paleozoic gn Paleozoic lgv Lower Paleozoic Zgn Late Proterozoic and lower Paleozoic Zg v Late Proterozoic and lower Paleozoic Zn Late Proterozoic Zv Late Proterozoic Yn Middle Proterozoic Yv Middle Proterozoic Xn Early Proterozoic Xv Early Proterozoic An Archean n Age uncertain Glacier, river, or water body Geologic contact Fault—Dashed where inferred Wisconsin glacial limit Normal fault Pre-Wisconsin glacial limit Thrust fault Low-angle detachment fault Strike-slip fault.