HAWAII 163 
the motion breaks up the hardened crust, piling the masses together 
either in slabs or huge angular fragments, according to the thickness 
to which the crust had cooled. It is probable that these clinker 
regions are sometimes over a fissure of ejection, and arise in these 
cases from a second outbreak after the previous flow has partially 
cooled. We thus account for their forming a narrow district, crossing 
a field of pahoihoi. If the motion of a lava stream be quite slow, the 
cooling of the front of it may cause its cessation, thus damming it up 
and holding it back till the pressure from gradual accumulation 
behind sweeps away the barrier. It then flows on again, carrying on 
its surface masses of the hardened crust,—some, it may be, to sink 
and melt again, but the larger portion to remain as a field of clinkers. 
The breaking up of the ice of some streams in spring, exemplifies 
imperfectly this subject, especially those instances in which the crust 
of lava is thin, and slabs are formed. But to obtain a just conception 
of the magnitude of the effect, the mind must bring before it a stream, 
not of the limited extent of most rivers, but one of five or ten miles in 
breadth: besides, in place of smooth and clear ice, there should be 
substituted shaggy heaps of black scoria, and a depth or thickness of 
many yards in place of a few inches.* 
Over the route to Kailiki the clinker districts were most extensive. 
Through part of the way, where the country was of this character, 
the natives had constructed a macadamized road five to six feet wide, 
by breaking down the smaller masses, which are almost as brittle as 
unannealed glass, and reducing the whole to fragments, over which 
* The clinkers formed at the eruption of Vesuvius in 1779, are well described by Sir 
William Hamilton. He says (Lyell’s Principles, ii. 177, from Otter’s Life of Dr. Clark), 
*¢ All lava, at its first exit from its native volcano, flows out in a liquid state, and is all 
equally in fusion. The appearance of the scoria is to be attributed only to the action of 
the external air, and not to any difference in the materials which compose it, since any 
lava whatever, separated from its channel, and exposed to the action of the external air, 
immediately cracks, becomes porous, and alters its form. As we proceeded downward, 
this became more and more evident ; and the same lava which, at its original source, 
flowed in perfect solution, undivided, and free from encumbrances of any kind, a little 
further down had its surface loaded with scorize in such a manner, that upon its arrival 
at the bottom of the mountain, the whole current resembled nothing so much as a heap of 
unconnected cinders from an iron-foundery.” The only error in the foregoing, is the 
statement that all lavas become scoriaceous, and covered with cinders, on exposure to 
the air. The pahothot regions of Hawaii are often more extensive than the associated 
clinker-fields ; and the latter occur on the same slope or plain with the former, where 
there is nothing but a variation in the rapidity of motion, or a renewal of movement from 
a cessation, to cause the difference. Other facts will be stated in the sequel. 
