Note upon the Brown Coal Formation of Washington Territory and Oregon.
BY WM. P. BLAKE.
Openings recently made in the coal formations along the Cowlitz River have shown the existence of several seams of brown coal, ranging from two to seven feet in thickness. They are separated by layers of sandstone, and are underlaid by a pebbly conglomerate.
The seven-foot seam contains a few partings of clay about six inches thick, but is chiefly a very compact coal, which breaks out in large blocks with a conchoidal fracture. It is very tough, and is not easily broken. It has the appearance of cannel or splint coal. Exposure to the sun and air causes it to shrink and crack.
It burns freely, giving a luminous flame, and a light smoke, similar to that from wood. The ignited coals hold fire in a remarkable manner, and with a strong draught or blast give an intense heat. A single fragment, when ignited, will continue to burn slowly to the center under an envelope of ash. A sun-dried sample gave me 50.8 per cent. of volatile matter, chiefly gas. The residue was a brilliant coke, the fragments of which were slightly adherent, thus showing a tendency to cake. Trials of the coal in quantity in open grates failed, however, to show any caking qualities. Some portions of the coal expand when burning and give a porous coke, which in many respects resembles ordinary charcoal.
This deposit appears to be formed in great part of trunks of exogenous trees. One trunk has been cut through that was over four feet in thickness: a part of this was compact coal, and another portion was in a half silicified state. Lines of annual growth may be seen in some of the samples. This combustible partakes of the characters of both coal and wood, and is in fact a highly condensed wood, carbonized, without the loss of its volatile portions.
Fossil plants are found in abundance in the adjoining sandy beds. They are chiefly leaves of deciduous trees, but there are some very distinct impressions of palms. This is significant of a warmer climate.
The same formation of brown coal appears to extend along the Columbia, back of St. Helen’s, where it is in close proximity to beds of iron ore, and the coal may perhaps be used to great advantage in the production of that metal.