Prof. Frazer explained by diagrams his new arrangement, by a side-hinged mirror, for illuminating intensely the whole field of the object under a microscope. A strong side light is reflected at a low angle from the under surface of a glass plate placed across the front of the objective, on to and again from the side mirror suspended from hinges, on to the object, and so back through the tube to the eye of the observer.

The minutes of the last meeting of the Board ot Officers and Council were read.

Pending nominations Eos. 893, 894, 895, and new nominations Nos. 896, 897 were read.

And the meeting was adjourned.

Stated Meeting, March 5, 1880.

Present, 17 members.

President, Mr. Fraley, in the Chair.

A letter accepting membership was received from Mr. Archibald Geikie, dated Geological Survey Office, Edinburgh, Feb. 2.

Letters of acknowledgment were received from the Natural History Society, Emden, dated Nov. 15 (102); the Royal Society of Luxembourg, dated Aug. 20 (102); the Societe Hollandaise, dated Harlem, Sept 20 (102, 103); and the Surgeon General's Office, at Washington, dated Feb. 20 (104).

Letters of envoy were received from the Trigonometrical

PROC. AMEK. PHILOS. SOC. XVIII. 105. 3B. PRINTED MARCH 30, 1880.

Survey of India, dated Dehra Dun, Jan. 20 : the Natural History Society, dated Eniden, Nov. 15; the Royal Saxon Society, dated Leipsig, Oct. 25; the Imperial Academy, dated Vienna, Dec. 1; the Societe Hollandaise, dated Harlem, Dec.; the U. S. Naval Observatory, aud Department of the Interior, dated Washington, Feb. 19.

A letter respecting Dr. Gabb's memoir was received from Mr. R. S. Swords, acting Librarian of the New Jersey Historical Society, dated Newark, March 3.

Donations for the Library were received from the Mining Bureau at Victoria; the Repertorium fur Meteorologie at St. Petersburg; the Academies at Berlin, Vienna, Rome, and Brussels; the Societies at Moscow, Stuttgardt, Halle, Giessen, Eniden, Bordeaux, Liege, and Harlem; the Swedish Bureau of Statistics; the German Geological Society at Berlin; the Geological Association at Dresden; the Revoe Politique; the Grand Ducal Institute at Luxembourg; the Minister of the Interior at Brussels; the London Astronomical, Geographical and Meteorological Societies; Society of Arts, and London Nature; the Essex Institute; the New York Academy of Sciences; the Brooklyn Entomological Society; the North American Entomologist; Dr. Wm. Elder; Mr. W. B. Taylor; the U. S. Department of the Interior; the Army Bureau; the Journal of Pharmacy, at Philadelphia; the Cincinnati Observatory; the St. Louis Public School Library; the Kansas Historical Society: and the San Francisco Mercantile Library Association.

An obituary notice of the late John W. Harden was read by Mr. Lesley.

The death of Gen'l Clement A. Finley, in West Philadelphia, September, 1879, was announced by the Secretary.

On motion the committee on the paper of X. Y. Z. for the Magellanic premium, was entrusted with the care of the document for examination, to report.

Mr. Ashburner exhibited specimens and photographs of Oil Sands, and read a paper on the constitution of the Brad

ford Oil Sand of McKean county, Pennsylvania. Remarks were made by Dr. Rogers and Mr. Lesley.

Prof. Frazer exhibited his microscopic reflector, made by Mr. Zentmeyer.

Mr. Frazer then discussed the principles of the problem of the popular 15 number puzzle with Mr. Briggs.

Pending nominations Nos. 893 to 897, and new nominations Nos. 898 to 901 were read.

On motion, the subject (postponed from the last meeting) of appointing delegates to assist at the Centennial Anniversary of the American Academy of Science and Art, at Boston, was referred to the President, Mr. Fraley, with power to act.

And the meeting was adjourned.

On the Constitution of the Bradford Oil Sand. By Chas. A. Ashburner, M.S., Asst. Second Geological Survey of Pennsylvania. ( With a plate.)

(Read before the American Philosophical Society, March 5, 1880.)

The constitution of the petroleum sands of Western Pennsylvania, which were discovered in Venango county twenty-one years ago, and which have ever since been producing mineral oil, is no doubt familiar to most of our geologists. The question suggests itself; in what way is the Bradford sand of McKean county, Pennsylvania, and Cattaraugus county, New York, dissimilar?

Before describing the structure of the sands, permit me to give some general facts showing the relative per centage of dry holes and the out-put of the producing wells in the two districts. At a glance, the comparison will indicate that some essential differences must exist in the sands and mode of occurrence of the oil, to account for the different results which have been obtained.

During the year 1879, there were 475 wells drilled to the Venango oil sands in the counties of Warren, Venango, Clarion and Butler; of this number 122 were dry holei or produced no oil; being 25.7 per cent.

In the Bradford or Northern district, there were during the same year, 2536 wells drilled to the Bradford oil sand, of which number but 76 were dry holes or only 3 per cent.; being nearly 23 per cent. less than in the Venango or Western district.

The average daily production, for the first month, of the wells drilled in the Bradford sand was about 20 barrels, while for the wells in the Venango sands it did not attain that amount.* When we take these facts into consideration, we can readily understand why there should have been 2536 wells drilled in the Northern district to only 475 in the Western.

Since the beginning of the year 1875, when the Bradford oil horizon was discovered, there have been 6249 wells drilled in the district, of which 236 were dry holes or 3.77 per cent. From the most authentic statistics which I can gather in the Western district, about one-fourth of all the wells which have been drilled in the Venango sands, since their discovery in 1859, have proved dry.

The Bradford sand consists of a gray and white sand, of about the same coarseness as the ordinary beach sand of the Jersey coast; compact, yet loosely cemented. The average thickness of the sand is about 45 feet, and from top to bottom, the sandy strata change but little in their general character. It is only when specimens from the successive layers are placed side by side and closely examined, that any difference in structure can be recognized. The grains of sand are angular, vary but slightly in size, color and the quantity of cementing material which holds them together in their rock bed.

The same lwmogeneousness, which characterizes the vertical section, is found to exist over a considerable horizontal area. In fact but little change is found to exist in the sand obtained from wells 15 miles apart, or in the sand from the intermediate wells.

The greatest length of the Bradford district is 18 miles north, 30° east; its greatest width is 12 miles in a north and south direction. The area of the territory is between 100 and 110 square miles. In this area the sand.is so regular and constant that if wells were drilled at random the number of dry holes, which would be obtained, would hardly exceed 2 in every 100. The percentage of dry holes spoken of as being obtained in the district includes those which were drilled outside of the probable oil territory and were genuine wild-cat wells.

In the Western district the characteristics of the Venango sands are quite different. The third or bottom sand, which is the most productive of the

* Some of the wells drilled to the Venango third oil sand have produced from 2000 to 3000 barrels of oil per day, while the largest well ever found in the Bradford district has not exceeded as many hundred. The largest individual wells have been located in the Western district; the largest average wells in the Northern district .

group, is sometimes thin, very fine, micaceous and muddy when taken from the sand pump ; in this condition it seldom produces any petroleum. This is the character of the sand at Pleasantville, where it contained only a trace of oil. The black oil of this district came from what was known as the stray or split third, occurring some 25 feet above the regular sand. Where the Venango sands are formed in thin layers, fme grained and clayey the driller views the territory with suspicion.

Note.—It must be remembered in comparing the sands of the two districts that they belong to different geologic formations. Based on lithological and stratigraphical facts, I make the Venango oil sand group the equivalent of the Red Catskill, No. IX (Old Red Sandstone), while the Bradford.sand is of Chemung age.

The following general section shows their relative positions:

See "Oil Sands of Penna.," Franklin Institute Journal, April 1878, also "Bradford Oil District," Transactions American Institute Mining Engineers, Vol. VII; by the Author. •

The accompanying illustration shows a typical specimen of a good producing third sand in the Venango group and a specimen of Bradford sand, such as might be taken from any of the producing wells in the Northern district. A productive Venango sand consists of a white, gray or yellow pebble rock; the pebbles being loosely cemented together and generally bedded in fine sand. The rock is open and porous. The interstices between the pebbles and sand grains are extensive and capable of containing a large bulk of oil; but this character does not maintain itself over any extended area. Areas of such sand are small and scattered and are separated by sand beds, possessing a character belonging to the unproductive sands.

The Venango sands are not homogeneous over any considerable area and are frequently very heterogeneous in section. The thickness of the sand varies; in one locality the upper part of the sand may be pebbly and of productive character and the lower part fine and contain no oili while but a short distance away the conditions may be reversed.

Such then are the principal features of the two great oil producing rocks of Pennsylvania.