Two classes of rock are to be discussed as occurring on Mount Rainier: the lavas and pyroclastics which compose the volcanic cone and the granitic rocks forming the platform upon which the volcano was built up.
The different textures of these lavas are doubtless expressive primarily of diversity in the physical conditions of consolidation, but also in part of variations in chemical composition.
In texture, the Rainier lavas are, for the most part, compact.
The lavas vary much in color and texture, but these megascopic differences are referable rather to the degree of crystallization of the magma than to its chemical character.
The latter lavas and tuffs may have originated from smaller and less important cones, now destroyed by erosion.
In petrographic character the lavas range from hypersthene-andesite to basalt.
But thelavas of Mount Rainier produce for the most part dark-hued flour, and as a consequence the rivers coming from that peak are dyed a somber chocolate brown.
On the eastern slope on the Wedge, between Winthrop and Emmons glaciers, the lavas are pyroxene-andesites and vary much in megascopic appearance, although little in microscopic characters.
Dense black rocks with abundant phenocrysts of glassy feldspars, rough and coarse lavas of different tints of pink, red, and purple, and compact light-gray rocks are some of the types represented upon the slopes of this volcanic cone.
Gibraltar is thus seen to be composed of interbedded lavas and pyroclastics, and on the Wedge a similar alternation is several times repeated, a pink agglomerate being exceptionally striking in appearance.
Vesicular lavas occur at several localities, and fragments of a light-olive pumice, many as large as a foot in diameter, wholly cover some of the long, gentle slopes southeast of Little Tahoma and in Moraine Park.
Wednesday 21st, was more quiet than the preceding days, though the lavas ran briskly.
I have seen antient lavas in the plain on the other side of Somma, which could never have proceeded from the present Vesuvius.
The most extensive lavasof Vesuvius do not exceed seven miles in length.
From the situation of this convent, it is clear beyond a doubt, that these lavas proceeded from the mountain called Somma, as they are quite out of the reach of the existing Volcano.
I mention this circumstance, as it may serve to point out true lavas with more certainty.
The ancient lavas of Ischia shew, that the eruptions there have been very formidable; and history informs us, that its first inhabitants were driven out of the island by the frequency and the violence of them.
The convent of the Madona del Arco, under which lavas have been found at 300 feet depth, and which must have proceeded from the mountain of Somma, when an active Volcano.
The annexed plans were taken upon the spot at this time, when the lavas were at their height; and I do not think them exaggerated.
There are some of these ancient lavas not less than two hundred feet in depth.
The Arenig rocks consist of black shales with interstratified beds of coarser sediment, and some thin lavas and ashes of intermediate type.
The Llandeilo beds of this area are chiefly of the nature of black shales, while the Caradoc series is represented by volcanic lavas and ashes of acid composition (felsites) with a few thin interbedded sediments.
The Merionethshire volcanic rocks consist of a great thickness of lavas and ashes of intermediate composition (anderites), associated with sandy and muddy sediments of no great vertical depth.
Two views as to the origin of the lavas have been put forward: according to Prof.
On the upturned and denuded edges of the Silurian strata a great pile of contemporaneous volcanic rocks of Lower Old Red Sandstone age rests unconformably, which consists chiefly of lavas with thin partings of tuff.
The lavas comprise dark pitchstone, resembling that at Kirk Yetholm, and porphyritic and amygdaloidal andesites and basalts.
Both the granite and the surrounding lavas are traversed by dykes arid sills of intermediate and acid types represented by mica-porphyrites and quartz-felsites.
The canyon is cut more than two thousand feet deep into the lavas and sediments, exhibiting the most fantastic carvings of erosion, modified by an exquisite blending of colors.
Iceland, with an area of forty thousand square miles, is a vast table-land from three thousand to five thousand feet in elevation, composed of volcanic rock similar to thelavas still ejected by its numerous volcanoes.
These rocks are the principal constituents of the lavas of the Andes, and the name was first applied to them by Leopold von Buch; but their representatives also occur in the British Isles, Germany, and elsewhere.
Thus we find that acid lavas have been generally extruded first, and basic afterwards--as in the cases of Western America, of Antrim, the Rhine and Central France.
The greatest known thickness of the lower zone of lavas is, as I have already stated, about 600 feet.
Dechen, there are sheets of basalt older than the greater mass of the brown coal formation, and others newer than the trachyte;[6] while dykes of basalt traversing the trachytic lavas are not uncommon.
It is impossible to determine with certainty what may have been the original thickness of the accumulated sheets of basic lavas with their associated beds of ash and bole.
We have now to consider the nature of the interior reservoir from which lavas are derived, and the physical conditions necessary for their eruption at the surface.
During the process of cooling from a molten condition, the heavier lavas would tend to fall inwards, and allow the lighter to come to the surface, and form the outer shell in both cases.
Throughout this vast area the volcanic lavas rest on an exceedingly varied rocky floor, both as regards composition and geological age.
We have fortunately abundant means of comparison, as the lavas of these two mountains have been submitted to close examination by petrologists.
On the other hand, the similarity of volcanic lavas over wide regions is strong evidence that they are drawn from one continuous magma, consisting of molten matter beneath the solid exterior crust.
I should say the gifts were, on the proper signal, dragged out of the field of food by a troop of young men, all with their lava-lavas kilted almost into a loin-cloth.
They are much interrupted, nevertheless, with abrupt, jagged precipitous gorges, which though offering instructive sections of the lavas for examination, would better be shunned by most people.
The glacial erosion of most of the Shasta lavas gives rise to detritus composed of rough subangular boulders of moderate size and porous gravel and sand, which yields freely to the transporting power of running water.
The lavas of the antient Solfatara volcano have been undoubtedly of a vitreous nature, and these appear at present argillaceous.
They roam mainly in the southwest corner of the Park, in the Falls River Basin, a level country fed by innumerable streams and springs coming out from beneath the lavas of the plateau.
Contemporaneous volcanic action is recorded by tuffs andlavas south-east of Limerick and north of Philipstown.
By an examination of volcanos now active, and by comparing their structure and the composition of their lavas with the ancient trap rocks.
On the 23rd of April, another full moon, the observatory instruments were agitated, the activity of the craters increased, and on the evening of the 24th splendid lavas descended the cone in many directions.
Interspersed between the flows of heavy lavas were other avalanches and showerings of volcanic ashes in great depth.
It provided an uplift of the land at the caldera, by the same means establishing a down-slope from the center outwards, along which the lavas of the eruption avalanched in fire and smoke.
Perhaps the soda contained in the lavas of the peak acts an important part in the formation of these deposits of silex.
It is only when lavasare covered with tufa and ashes, that the volcanic islands, losing that appearance of nudity which marks their origin, bedeck themselves in rich and brilliant vegetation.
Between Vauclin and the feldspar-lavas of the Paps of Carbet is found, as M.
Wherever these lavas are scorified, and where they have a shining surface, as in the basaltic mounds to the north of Lancerota, the development of vegetation is extremely slow, and many ages may pass away before shrubs can take root.
In the plain of Retama, the basaltic lavas disappear under heaps of ashes, and pumice-stone reduced to powder.
They no more belong to the soil where they lie, than the feldsparry lavas of Etna, seen in the pavements of Hamburg and other towns of the north.
They are usually ascribed to a progressive accumulation of liquified matter, and the diffusion of lavas issuing from a central mouth.
Vesuvius, during a long series of years, has also thrown out lavas without leucites: and if it be true, as M.
The lavas which are not covered with volcanic ashes remain for ages without any appearance of vegetation.
At Vesuvius also, we perceive small crystals of vitreous feldspar only in the very ancient lavas of the Somma.
In this region the lavas which fill the ancient basin of the park rest upon the flanks of mountains formed of fragmentary volcanic ejecta, .
The gas is probably generated by the action of the acid water on the ancient limestones that here underlie the lavas at no great depth; outcrops of these limestones occur only a few miles away at the mouth of Soda Butte Creek.
Defn: Resulting from, or produced by, the action of fire; as, lavas and basalt are igneous rocks.
Defn: A mineral occurring in small yellow crystals, found in the lavas (melilite basalt) of Vesuvius, and elsewhere.
When we remember how rapidly the top of many glassy lavas cool down we can understand that they have often only time to grow very small.
Fouque and Levy, have actually made lavas and shown us how it is done in Nature.
In the clinkers above, where the cooling goes on very rapidly, the lavas formed are semi-transparent and look much like common bottle-glass.
These are dark slates and thin-bedded grits with enormous masses of interbedded igneous rocks, lavas and ashes, the product of contemporaneous volcanoes.
In the Lough Mask district beds of this age are found, as in Wales, interstratified with volcaniclavas and tuffs.
In the Snake River Valley the latest lavas are much younger (Quaternary).
Sketch of a mountain range along Skolat Creek, Alaska, showing Tertiary lava beds resting upon deeply eroded tilted limestones and lavas of late Paleozoic (Carboniferous) Age.
The present topography has been produced by erosion since the Tertiary lavasflowed out.
Lavas are classed, according to their structure, as scoriaceous or cellular, glassy, stony, etc.
Magnetite is present in all of the lavas here described.
The Mineral Constitution and Microscopic Characters of some of the Lavas of Etna.
Illustration: Sections of Etna Lavas seen under the Microscope] Plagioclastic felspars are unquestionably the dominant constituents of these lavas.
A cursory examination of the series of specimens collected by Mr. Rodwell, seemed to show that all the lavas of Etna, irrespective of their differences in age, exhibit a remarkable similarity in mineralogical constitution.
Rose was the first to prove that the lavas of Etna do not contain ordinary felspar (or potash felspar), but labradorite (or lime felspar.
An account of microscopic analysis of some of the lavas of Etna, for which I am indebted to Mr. Frank Rutley, will be found appended to this chapter.
No true estimate can be obtained from the observation of the decomposition of lavas, for it has been often observed that two lavas will decompose at very different rates.
Ancient lavas forming the escarpments around the Val del Bove; and 6th, Modern lavas.
To the presence of this substance much of the opacity of thin sections of the Etna lavas is due.
Mr. Rutley's examination of Etna lavasunder the microscope.
Magnetic oxide of iron is very visible in thin slices of the lavas when placed under the microscope; and iron appears to be a constant constituent in nearly all the products of the mountain.
Its surface is the top of a vast accumulation of lavas in places over a mile thick.
The contact lines between lavas and buried surfaces in the deep Majes and Cotahuasi valleys are in places excessively serrate.
It is strongly developed about Huadquirca and Antabamba and, still associated with a quartzite floor, it finally disappears under the lavas of the great volcanic field on the western border of the Andes.
The above list will hopefully give you a few useful examples demonstrating the appropriate usage of "lavas" in a variety of sentences. We hope that you will now be able to make sentences using this word.
