cemented together and forming a limestone mass of such interest that several large pieces were dug out for exhibition in the Museum.

Dr. Bassler then proceeded to the Lancaster Valley of Pennsylvania where, in company with Dr. Resser, some days were spent studying the stratigraphy of the valley, and collecting minerals and fossils. Working in the region of highly metamorphosed rocks in southern Lancaster County, they were fortunate enough to secure intact the large mass of finely banded, crinkled limestone shown in figure 23, L. This illustrates, on a small scale, the folding to

which the earth's crust has been subjected and forms a much needed addition to the exhibits. Proceeding to York, Pennsylvania, an effort was made to determine the stratigraphy of that area from which numerous Lower Cambrian fossils had been collected for the Museum in former years. An idea of the general structure was obtained, but the stratigraphic details were worked out by Dr. Resser on a later trip.

The east front of the Alleghany Mountains was then visited by Dr. Bassler in an effort to obtain exhibition specimens illustrating fault

ing and its accompanying phenomena. In western Maryland a fault passing through a Silurian conglomerate was located. The conglomeratic layer itself at this place was composed of small, rounded pebbles of pure white quartz, forming an interesting educational object in itself, but along the fault zone the conglomerate had been broken into angular fragments and recemented together into a hard rock. In one case this recementation had been caused by silica and in another by iron ore. Large examples of both kinds of this fault breccia, as it is known technically, were quarried out. Fortunately,

as shown in figure 24, this fault zone (C) outcropped along a good country road, making the problem of quarrying and transportation

easy.

In each of these areas photographs of the occurrence of these specimens in nature were secured so that the explanatory exhibition labels can be illustrated. The object of displaying such specimens is not simply to illustrate their geological or paleontological features, but to show in the same exhibit a portion of geological history involving at least several distinct events.

Following this Appalachian work, Dr. Bassler spent some days in central Kentucky and eastern Indiana searching for certain exhibits. In Kentucky he located a layer of limestone which had been so carved out by underground water that it could be used to illustrate the formation of a cave in miniature, and a suitable piece was quarried out. Certain fossil faunas which were much needed to complete the Museum's paleontological material from this area were also secured. The main object of the work in Indiana was to obtain a large slab of limestone composed entirely of certain characteristic brachiopods known to all beginners in paleontology, fre

quent requests for such exhibits having been made by students visiting the Museum. After a week of search, two large, well-preserved slabs of this kind were found, but in an area some miles from a railroad. Upon endeavoring to have them transported to a freight station it was found impossible to procure help of any kind. These two specimens were therefore buried deep enough to insure their safety until such time as they can be shipped to Washington.

Dr. Charles E. Resser spent a part of his vacation studying the detailed stratigraphy of the Lower Cambrian deposits of the Lancaster and York valleys of Pennsylvania. He found that the lowest

sedimentary rocks of the region were massive, unfossiliferous limestone probably of Pre-Cambrian age, with a great erosional unconformity at their top. Immediately following this unconformity is an arenaceous limestone several feet thick containing the Corynexochus fauna hitherto believed to be of Middle Cambrian age. Following this bed, in apparently normal succession, are the well-known Lower Cambrian shales containing Olenellus and other trilobites. In figure 25 the point of contact between the two Lower Cambrian formations is indicated at C. Collections of two faunas of Lower Cambrian age were secured during these studies.

FIG. 26.-Open iron ore pit at Cornwall, Pa. Photograph by Resser.

Dr. Resser also spent some days in collecting mineral specimens from the celebrated ore banks at Cornwall, Pennsylvania, a locality famous for its well-preserved minerals, but unfortunately poorly represented in the Museum collections. These ore banks are in the hills between Lancaster and Lebanon counties and, as they have been worked since 1853, they are now great open pits from which the minerals can be obtained. The ore is the iron oxide magnetite, formed along the lines of contact of an igneous mass intruded into Paleozoic limestone. The magnetite often occurs well crystallized, but the mineralogical interest of the locality lies in the minerals of copper, iron, and magnesium silicates which were formed with the magnetite. The photograph (fig. 26) shows the arrangement of

rocks in one of the open pits with the ore bed (O) at the bottom, above this the Early Paleozoic limestone (P), and capping the limestone, the red beds of Mesozoic age (M).

FIELD-WORK OF THE SMITHSONIAN ASTROPHYSICAL
OBSERVATORY

As usual, for some years past, the Astrophysical Observatory maintained its observing station on Mount Wilson and the work was in the hands of Mr. L. B. Aldrich. As heretofore, the principal object was to follow by accurate measurements the variations in the radiation of the sun as that would be found if one were on the moon, for example, outside the earth's atmosphere. The season did not prove particularly favorable for this work on account of unusual cloudiness. Nevertheless, Mr. Aldrich made many solar-constant observations that will be unusually valuable on account of the possibility of comparing them with similar observations made in South America, which will be related below.

It happened that a station of the U. S. Aviation Service was located near Mt. Wilson, at Arcadia, and military balloons not infrequently passed up through the layer of fog which often covers. the San Gabriel Valley, lying between Mount Wilson and the sea. It occurred to Mr. Aldrich to take advantage of this condition of affairs to make a measurement of the reflecting power of such a great layer of fog with a view to the applicability of such measurements to a consideration of the temperature of the planets Earth and Venus, both of which are to a large degree covered with clouds. We have at the Astrophysical Observatory an instrument called the pyranometer, devised by Messrs. Abbot and Aldrich for the purpose of measuring the heating effect of radiation received from a whole. hemisphere. For example, the heat from the sun and sky combined, or from the sun alone, or from the sky alone, as it falls upon a horizontal surface may be determined by this instrument. Mr. Aldrich's plan, therefore, was to expose the pyranometer upright to the sun and sky combined, and inverted to the radiation coming up from the layer of fog. For this purpose he needed a support for the pyranometer above the fog, and such a support he thought might be furnished by a military balloon.

With the approval of General Kenley the investigation was made on a favorable day in September, when the upper and lower surfaces of the fog lay respectively about 2,800 feet and 1,000 feet above the ground. Two officers and 50 men being detailed to aid