pumiceous

They are about a million years old and made up of pumiceous cross bedded brown and yellow clayey sands.

Later, slower flows came directly from the new north-facing crater and consisted of glowing pumice bombs and very hot pumiceous ash.

It is a grey or cream-coloured fragmental rock, largely composed of pumiceous dust, and may be regarded as a trachytic tuff.

Volcanism during the Holocene produced a series of pumiceous tephras, tuff rings, lava domes, and lava flows.

The lower member consists mainly of unwelded (unjoined), but heavily compacted, pumiceous lapilli-tuff and crystal tuff strata.

In the Eifel region of Germany a trachytic, pumiceous tuff called trass has been extensively worked as a hydraulic mortar.

Rhyolite tuffs contain pumiceous, glassy fragments and small scoriae with quartz, alkali feldspar, biotite, etc.

Half way up was a square enclosure of some greyish stone, which I found subsequently was built partly of coral and partly of pumiceous lava.

They can occur in welded pyroclastic fall deposits and in ignimbrites, which are the deposits of pumiceous pyroclastic density currents.

They produced a widespread phreatomagmatic pumiceous tephra deposit, obsidian flows, large and small pumice cones, and a pumice ring.

The elongation of the microvesicles occurs due to ductile elongation in the volcanic conduit or, in the case of pumiceous lavas, during flow.

An eruption of Laguna Xiloá 6100 years ago produced pumiceous pyroclastic flows that overlay similar deposits of similar age from Masaya.

The Tassajara Formation consists of sediments ranging from brown to gray mudstone, andesitic sandstone, conglomerate, and minor bentonitic and pumiceous tuff.

Chapter V.--Curious pumiceous infusorial mudstone (page 118) of Patagonia; climate of old Tertiary period, page 134.

On the south-west flanks of the mountain, deeply incised rivers expose a major industrial mineral resource of pumiceous tuffs, which provide much high-quality building stone to Nyeri and the surrounding densely populated countryside.

Vitric ash particles from high-viscosity magma eruptions are typically angular, vesicular pumiceous fragments or thin vesicle-wall fragments while lithic fragments in volcanic ash are typically equant, or angular to subrounded.

This area of pumiceous tuffs is only a small part of a much larger blanket of Pliocene ignimbrites covering more than 20 000 square kilometres, which originated from a catastrophic eruptive phase in the central sections of what is now the Kenya rift.

Pliny's account naturally didn't go into the details of the mechanics of the eruption, but his account is so illuminating that it is quite clear what happened, and similar eruptions, blasting large volumes of pumiceous ash into the air are still called Plinian eruptions.

Rhyolite tuffs contain pumiceous, glassy fragments and small scoriae with quartz, alkali feldspar, biotite, etc. Iceland, Lipari, Hungary, the Basin and Range of the American southwest, and New Zealand are among the areas where such tuffs are prominent.

Glassy forms of trachyte (obsidian) occur, as in Iceland, and pumiceous varieties are known (in Tenerife and elsewhere), but these rocks as contrasted with the rhyolites have a remarkably strong tendency to crystallize, and are rarely to any considerable extent vitreous.