BALA SERIES

bala series, in geology, a series of dark slates and sandstones with beds of limestone which occurs in the neighbourhood of bala, merionethshire, north wales. it was first described by a. sedgwick, who considered it to be the upper part of his cambrian system. the series is now placed at the top of the ordovician system, above the llandeilo beds. the bala limestone is from 20 to 40 ft. thick, and is recognizable over most of north wales; it is regarded as the equivalent of the coniston limestone of the lake district. the series in the type area consists of the hirnant limestone, a thin inconstant bed, which is separated by 1400 ft. of slates from the bala limestone, below this are more slates and volcanic rocks. the latter are represented by large contemporaneous deposits of tuff and felsitic lava which in the snowdon district are several thousand feet thick. in south wales the bala series contains the following beds in descending order:--the _trinucleus seticornis_ beds (slade beds, redhill shales and sholeshook limestone), the robeston wathen beds, and the _dicranograptus_ shales. the typical graptolites are, in the upper part, _dicellograptus anceps_ and _d. complanatus_; in the lower part, _pleurograptus linearis_ and _dicranograptus clingani_. in shropshire this series is represented by the caradoc and chirbury series; in southern scotland by the hartfell and ardmillan series, and by similar rocks in ireland. see caradoc series and ordovician system. balash (in the greek authors, balas; the later form of the name vologaeses), sassanian king in a.d. 484-488, was the brother and successor of p[=e]r[=o]z, who had died in a battle against the hephthalites (white huns) who invaded persia from the east. he put down the rebellion of his brother zareh, and is praised as a mild and generous monarch, who made concessions to the christians. but as he did nothing against his enemies, he was, after a reign of four years, deposed and blinded, and his nephew, kavadh i., raised to the throne. (ed. m.)