Bala Beds.

Bala Beds. The rocks of the Bala district, North Wales, contain two limestones, separated by some 1400 feet of arenaceous and slaty strata. The lower limestone (25 feet) is called the Bala limestone, and has been followed over a considerable area; the upper, or Hirnant limestone, is local. The lower, or Bala limestone, is supposed to be the same as the Coniston limestone of Westmoreland. Bala beds form a group of the Lower Silurian. In the Snowdon region they attain a great thickness, and show intercalated sheets of felsitic lava and tuff, bespeaking long-continued volcanic action. See SILURIAN.