breadth, are marked with the days of the year; the horizontal lines serve as divisions of arbitrary scales of the variable quantities which enter into the furnace record, the scales being written in figures at each end of the sheet.

Each day, after entering in the furnace book the usual record of charges, fuel, ore, flux, revolutions of engine, temperature and pressure of blast, quantity and grade of product, etc., the clerk enters these same variable quantities upon the diagram sheet, by making a dot or mark for each variable on the vertical line representing the day; the position of the dots on the line being determined by reference to the scales at the end of the sheet. The dots entered from day to day representing each variable are joined by straight lines, making thus a continuous irregular line or diagram. The magnitude and position of the arbitrary scales at the ends of the sheet are determined to suit convenience, so that the irregular lines representing each variable will not crowd or interfere with each other. The time necessary for keeping such a graphic record, if the furnace book record is properly kept, should not be more than one or two minutes each day.

Regularity in quantity and grade being a chief requirement in working a blast furnace, it is desirable to know what quantitative effect changes in each of the antecedent conditions of the first two classes above mentioned have upon this result, so that the furnace manager may know how to control the working of the furnace, by first knowing the effect of a change in those conditions over which he has no control-as changes in the atmosphere-and, secondly, how and to what extent he can counteract these effects by making changes in those conditions over which he has control.

If all the ordinarily variable antecedent conditions in the working of a blast furnace should become constant, the quantity and grade of product would be constant. If all conditions remained constant, except the atmosphere, the quantity and grade would change with the atmosphere, and the furnace manager, who, by experience, had become acquainted with the effect of changes in the atmospheric conditions, might, on observing an atmospheric change, predict or prevent the change in the working of the furnace, without waiting for it to be made known to him by a change in the appearance of the cinder, or of the iron in the pig bed.

The graphic method of recording the variable conditions and results which attend the working of a blast furnace, offers to the furnace manager a valuable auxiliary to aid him in his observation

and study of the effects of changes in the variable antecedent conditions above mentioned upon the variable results. By it also he can study the effect of arbitrary experimental changes in the method of working a furnace, or the results of two furnaces differing in any of their features. The accompanying diagrams (Plate XII) are so irregular that they seem to follow no law, and it could scarcely be expected that any important deductions could be made from the record of only a single month; but there is one peculiarity of the diagram, representing average grade, which may be worthy of attention.

From the 19th to the 26th of the month, there is a rapid fall of the average grade from 1.13 to 2.65. The cause of this fall appears to be indicated by the atmospheric record. The temperature rises, from the 19th to the 22d, from 28.7 to 48 degrees; the percentage of vapor in the atmosphere rises, from the 18th to the 24th, from 0.40 to 0.62 per cent., and the barometer ranges lower during the same period than at any other portion of the month. The revolutions of the engine remaining constant, these atmospheric changes would cause a chilling effect upon the furnace, and a fall in grade of the iron.

It is not my intention, however, to discuss here any theory of furnace working, but merely to point out the value of the graphic method in studies of this kind, which should insure its adoption at every furnace.

BY WILLIAM P. BLAKE, F.G.S., NEW HAVEN, CONN.

(Read at the Amenia Meeting, October, 1877.)

EUREKA has for several years past been known as one of the most important centres of production of argentiferous lead in the country. The average daily yield is now one hundred tons of lead bars, in which the silver and gold of the ore is concentrated. The value of this lead, called "bullion," is about $300 per ton. To produce this quantity of metal, about four times the weight of ore, or say four hundred tons, is required. Most of this ore is supplied by the two leading mines of the district, the "Eureka" and the "Richmond," adjoining claims on Ruby Hill, about two miles from Eureka. There are, however, many other mines from which considerable quan

tities of ore are taken, and which are apparently similar in nature and extent to the two first named. Among these are the "K. K. Consolidated," adjoining the Eureka, the "Jackson," "Bald Eagle," "Pioneer," "Hamburg," and others. Few districts can show so many claims, yielding ore from the surface downwards, and in most cases in quantity sufficient to fully pay the cost of opening and the erection of machinery and buildings.

The claims are in a belt of country extending some six miles southward from Eureka, along a line of hills, known in the order of their succession, southwards, as Adams Hill, Ruby Hill, McCoy Hill, and Prospect Mountain; the first being the lowest adjoining the plain, and the last named, rising to the height of about 10,000 feet above the sea.

The rock formations are chiefly limestone, in part, or perhaps wholly dolomitic or magnesian. There are, also, quartzites and strata of shaly limestone, and shale. The central portions of McCoy Hill, and of Prospect Mountain, are formed of more or less crystalline limestone, of light color, in places affording cleavage rhomboids, measuring two or three inches on a side. The stratification is obscure. Fossil trilobites have been found upon the eastern flank of Prospect Mountain.

This subcrystalline nucleus of Prospect Mountain and McCoy Hill, is flanked on the east and north by quartzite, magnesian limestone, and shale in succession, forming apparently an anticlinal fold, of which the upper portions and the western side, if any existed, have been swept away. The magnesian limestone between the quartzite and the shale is regarded as the chief ore-bearing formation. It is in this stratum, at the north end of McCoy Hill, that we find the Eureka and Richmond mines. At this point the limestone is thicker and more prominently exposed than elsewhere, forming bold rocky outcrops of an ashy-gray color. Inspection on the surface, and below, shows that the rock has been, and is now, much shattered and broken, the older fractures being indicated by a network of small white veins of calcite, by which the fragments of rock once separated have apparently been cemented and held together. It is not common to find large unbroken masses of the rock preserving its stratification. In most of the drifts of the mines it can be picked down as if it had been previously shattered and crushed to fragments. Cavities and open, fissure-like spaces exist, and caverns of considerable size have been found. In such openings even at great depths, strong draughts

of good air show that the open spaces have some connection, though distant, perhaps, with the outer air.

It has been assumed that this fragmentary condition of the rock is the result of the folding at the time of the original uplift. But such movements are not necessarily attended with fracture and crushing. It seems much more probable that subsequent, and perhaps, recent movements, have shattered the rocks. There is abundant evidence of such movements. Smooth wall-like surfaces are frequently encountered in drifting. Some of these surfaces are highly polished and striated. Seams and layers of finely brecciated rock are also found.

There are also evidences of movement outside of this special stratum of magnesian limestone. Its plane of contact with the shales is marked by thick layers of clay, compressed, rubbed, and stratiform; inclosing at the same time nodules and pebble-like masses of the adjoining harder rocks. In some places this clay is several feet in thickness, notably in one of the drifts of the Richmond Mine. Some of the clay layers there are remarkable for their extreme toughness, and a certain degree of elasticity, like thick masses of leather, due apparently to the lamination produced by rubbing and pressure. This clay septum has been regarded by some as evidence of the existence of a lode. It certainly resembles the clay walls of large lodes, and recalls to mind the divisions of the eastern wall, or walls, of the Comstock lode. But it by no means follows in this case, at the Eureka mines, or elsewhere, that a clay wall or septum bounds, and marks a lode. It simply marks a plane of least resistance to the movement of the rocks, one upon another, and is the result of the attrition of the rocks. Such planes of movement are not necessarily accompanied by mineral emanations, or by the formation of veins. We may believe that they exist in all rock formations, especially where, as in earthquake countries, the rocks may be regarded as in almost constant motion.

The underlying quartzite also merits our attention as an important member of the series of strata. It is a formation of considerable magnitude, and may be traced for miles southeastward from Ruby Hill, presenting generally an outcrop much stained with iron oxide. In the Ruby Hill mines it is noteworthy for its uneven surface, often projecting outwards into the overlying limestone in great bosses, folds, or "capes," as they are sometimes called by the miners and surveyors. This highly irregular surface has been explained by