▁quality , ▁and ▁although ▁there ▁were ▁some ▁ 3 0 ▁sl ate ▁mines ▁on ▁the ▁land , ▁of ▁varying ▁sizes , ▁this ▁sl ate ▁was ▁not ▁of ▁a ▁particularly ▁good ▁standard , ▁much ▁of ▁it ▁more ▁su ited ▁to ▁sl abs ▁than ▁roof ing ▁sl ate . ▁Nor ▁was ▁production ▁high , ▁and ▁the ▁output ▁of ▁all ▁the ▁quar ries ▁over ▁the ▁ 1 5 0 ▁years ▁of ▁their ▁existence ▁total led , ▁for ▁instance , ▁just ▁two ▁years ' ▁worth ▁of ▁output ▁from ▁the ▁Bla en au ▁F fest ini og ▁quar ries . ▁ ▁Prior ▁to ▁the ▁arrival ▁of ▁the ▁railway ▁in ▁the ▁ 1 8 6 0 s , ▁most ▁sl ate ▁was ▁carried ▁by ▁cart ▁to ▁the ▁qu ays ▁at ▁T ref ri w . ▁The ▁estate ▁also ▁owned ▁a ▁number ▁of ▁min eral ▁mines , ▁mostly ▁in ▁the ▁area ▁of ▁today ' s ▁G w yd ir ▁Forest . ▁ ▁The ▁principle ▁quar ries ▁on ▁the ▁Est ate ▁were ▁located ▁around ▁Dol wy dd el an ▁where ▁a ▁syn cl ine ▁com pressed ▁the ▁N od ▁Glas ▁mud st ones ▁into ▁sl ate ▁ve ins . ▁These ▁were ▁the ▁Prince ▁L le wel lyn , ▁Ch ware l ▁D du , ▁Ty ' n - y - b ry n ▁and ▁R hi w - go ch ▁quar ries . ▁ ▁Much ▁of ▁the ▁estate ▁was , ▁however , ▁under ▁continuous ▁mort g age , ▁and ▁in ▁ 1 8 9 4 ▁Dol wy dd el an ▁was