Agglomerate size is 1 - 40 µm with average pore size is > 30 nm.
Sir A. Geikie has shown that the puy type of eruption was common in the British area in Carboniferous and Permian times, as abundantly attested in central Scotland by remains of the old volcanoes, now generally reduced by denudation to the mere neck, or volcanic vent, filled with tuff and agglomerate, or plugged with lava.