|
I 1 1 111 11 WWI 1:21 11 1111 1
<br />MODIFIED FROM MURPHY, J.R., 1979, GROUNDWATER RESOURCES OF LOUDOUN COUNTY, VIRGINIA,
<br />VSWCB PLANNING BULLETIN 315.
<br />Light grey to greenisn grey phyllite interbedded
<br />with layers of fine- g -ained quartzite, locally
<br />calcareous, some graywacke and medium to thick-
<br />headed, coarse- grained quartz sandstone.
<br />Light grey -tre-white, fine - grained, finely -
<br />laminated -to- bonded quartzite. Some quartz -
<br />pebble conglomerate, pebbly quartz sandstone,
<br />and very sericitic sandstone, phyilite and sandy
<br />phyilite.
<br />Interbedded, reddish- purple, tuffacaous
<br />phyilite; dark -green metabasalt; white, pink and
<br />tan rhyolitic metatuff, epidotized quartzote
<br />meta - sediments; netabasalt, basaltic flow
<br />breccias, epidosite and purple amygdaloidal
<br />slate.
<br />Het= ,.
<br />rogenous unit of metagraywacke, mea artese,
<br />and phyllites. Overall texture ranges from
<br />gneissic boulder beds upward ,,.,rough cobble beds
<br />and arkoses to cross- bedded, .-odium- grained
<br />arkose and platy - bedded sandstone.
<br />Light -to -dark gray, medium- graned granitic
<br />rock, including quartz monzo -i,e syerl
<br />granite and acner oneiss. Felsic and natty dike
<br />intrusions,
<br />With gray to black fossilikerous shales and siltslones, and
<br />with conglomerate composed of basalt, greerstone, and
<br />schist pebbles- Unit is jointed but mostly resistant to ero-
<br />sion, forming gently rolling uplands and locally steep
<br />bluffs- Residuum and soil are thin and sandy
<br />0-nn QUARTZ CONGLOMERATE —Red to purplish -brown and
<br />darli-greensih gray, pebble cobble and bo ;Jar con-
<br />glomerate h vinq a poorly sorted tilly san(i inadix, inter- b
<br />bedded with red brown ar{,o nc ,andvone and purplish
<br />brown bandy tilnuons Claris are mainly subrounded to
<br />angular quarts quartzite, and schist in t,ee eastern pail of
<br />the baste; subrounded greenstonv ftasah, tTrnestone,
<br />phyilite, and quarizlle clasts In the u.eru Conglomerate is
<br />commonly deeply weathered and loosen the east, indu-
<br />rated except where deeply weathered in the west. Re-
<br />rouurtl'is thick and saprolibc an<t so -1 u fine and gr©velly,
<br />commonly with coarse lag gravel at th t t i
<br />S4 b -m LIMES] CONGLOMERATE— Dominai di ay ebble
<br />and cobble conglomerate with a reddiciI biomn to gray
<br />sandy, silty, or limy matrix and calcite e emeat. tncnbed
<br />dell with thin lenses or beds of reddish linco c, calcareous
<br />sandstone or siltstone- Clasts are mos t� sumounded to
<br />angular dolomite or limestone with ❑r nnr xhist, phyllNe �
<br />or siltstone. Und Is extremely susceptible to sohilorn, par-
<br />ticularly on exposed faces and moils ydiets ;;;r fractures.
<br />Residuum isrc:d - blown, none ciucareous, s ltv and sandy
<br />w clay_ Thickness of residuum is extnmelt variable It is thin
<br />or absent on low_ linear strike ridges ofmasaive conginm-
<br />erate, but may be very thick In parallel swaies I,here
<br />conglomerate is intensely Janted and d"sotved or there
<br />interbedded with siltstone, The bedrock surface beneath
<br />the swaies is Irregular, with pits, ridges and pinnacles of
<br />rock which produce relief of b m or more on the bedrock
<br />surface , an
<br />?irmty cemcined by silica. Claris moony sur-oraeded tb
<br />angular graen.stone with minor suboaunded qua izlte
<br />and vein quartz. Conir y Corr c steer becrosiI buffs, .
<br />out rolling upland surfaces may cm manhed by moder-
<br />ately thick saproialc residuum oln' 5C3Ucn1d core
<br />stontic Soil is till. reddish trou , sla and clayey
<br />oaf°
<br />THERMALLY METAMORPHOSED R0CK t =tine➢;
<br />metamorphose sedimentary rocks ur undmy
<br />dtairl intrusive bodies. Rkd bnnrr n n,-cn.e arw
<br />shale hornfels are bleached to vanous shades ci
<br />mauve, buff, or green -gray, commonly strand - Thew
<br />rocks nave been baked in great tosdeness, and
<br />mineralization is common along jaunts or f- a In
<br />blabs wtuar, the rocks, or wirtin dusts let .neramor-
<br />priosect conglomerate. Typical c arne;n i c con¢ 5
<br />In the unit include voluble, colrdlerue, meta i c miner-
<br />als pyroxene, or garnet. Beans cs mcot well
<br />preserved. Residuum. is generally thic, so e item
<br />and gravelly- Commonly forms t pla,s n , o :gnr'r
<br />than adjacent dlabase
<br />DIABASE inhusive dikes, stock arni situ u ;es of
<br />dense, nand, dark -gray to black , itirreois
<br />cock havinga medium 3exRrre ant, ai ;.igrany
<br />'or fabric of interlocking subhedrat cldspar ago
<br />pyroxene- irregular pods and pcgater'n,c celns of
<br />granophyre are common ;n larger dorbase 000 -C, Over -
<br />{ain by reddlsd to yellowish Drown and Q17c, cSa1c -rich
<br />residuum as much as 10 in r, ck, commonl, cor-iaiMgy
<br />spneroidaliy weathered core stones or Eery ;cesn rock.
<br />IJnli commorny Forms modular unon;l e, jeugraphy, 0u4
<br />locally underlies lowlands and va ieys
<br />PRE TRIASSIC ROCES— l)ndivn. e = sc ns phyilite,
<br />quarune, greenshuds, limestone, c .neit s sane. Cmn-
<br />moniy foliated and cleaved and percaave3y jointed: thick
<br />saprolont cover, except hard and *. where exposed in
<br />Cliffs or sucaae cuts Soils commonly thick silt ioarns cx-
<br />eopt on uplands underlain b ,u elite ,sc ;dy soles} or
<br />greenswror icaayey soils`!
<br />U — UPTHROWN BLOCK
<br />D _, DOWNTHROWN BLOCK
<br />4000 METERS
<br />6-18 + ��
<br />r®Jnsg inc. t _.
<br />GROUNDWATER SPECIAUSTS
<br />GEOLOGIC SETTING OF THE PROPOSED
<br />LOUDOUN COUNTY, VIRGINIA
<br />PREPARED BY
<br />R.M.C.
<br />DATE: 6/19/89
<br />PLATE
<br />CHECKED BY
<br />: R.M.C.
<br />REVISED
<br />I
<br />DRAWN BY :
<br />R.J.T.
<br />DRAWING NO:P8775- 000 /iCD13
<br />
|