log n' z(1+bt) log y'

if the same corona, 2, and time interval, t, is implied.

Hence (log n) = 8 (logy) while n = (6m/πα)s' = 1208'. Therefore log y'/log y = (log 4+3 log s′)/(log A+3 log s). ann/6m are given in the chart, curves 1, 2, 3. From the latter for s = 5.0, 8' 8.0 to 9.0cm. Hence

The computed values &

=

whereas y

819 was the value computed in my work on coronas for the exhaustion 76-58cm.

Since roughly y= (p/p.)1/, where p = 76 and y = 1·4, the following values of dp obtain:

Thus if the pressure decrement on exhaustion had been taken 1em higher than the observed value, the apertures computed from successive exhaustions in the former memoir would agree with the average apertures directly measured in the present paper. Observationally this is out of the question, but it is nevertheless difficult to know just what pressure is effective in the adiabatically cooled receiver (cf. Structure of the Nucleus, p. 38, § 16), since neither the isothermal nor the adiabatic conditions will rigorously suffice. The memoir shows that isothermally y 764; adiabatically y = 825; adiabatically with allowance for condensed water y=819, as already specified. The present aperture data demand y = 805, which is even nearer to the isothermal y than the value taken.

Incidentally one may note the precision with which y must be entered or the pressure difference determined, if the observations are to be sufficiently close to admit of a computation of d and n. In other words, it is probable, that the ratio y may be determined with greater accuracy from the successive apertures as a whole, notwithstanding their periodic character, than by direct measurement. This is what I meant by stating that the two sets of observations would probably sustain each other, for nobody would be justified in using the apertures of abnormal coronas, unless such use was suggested and guided by independent evidence. My own conviction is that n'=2.2 n may now be accepted with confidence.

8. Summary. The result of this paper is then favorable to the use of the apertures of coronas in place of the colors of the annuli, for estimating the number of particles corresponding to *Structure of the Nucleus, chapters 3 and 4, this Journal, xiii, p. 83, 86.

a given degree of supersaturation at a given temperature. Full allowance must, however, be made for the occurrence of periodic variations of aperture in relation to the diameter of the fog particles; in other words, a given aperture is only of value when qualified by the type of corona (whether of the crimson or green order) to which the aperture belongs. Thus it will not in any case be possible to dispense completely with the color pattern. It is with the object of finding these corrections systematically that I have recently begun a series of experiments with a new form of plate glass apparatus and shall then refer to other developments. Homogeneous light, though in many respects desirable, gives effects so faint as to be useless in practice.

With the above data I am able to make an independent estimate of the number of particles in the saturated phosphorus emanation. The number found for the first fog of the series was (Phil. Mag. (6), iv, p. 25, 1902) n = 83,000; since n'= 2-2 n, n'= 183,000 particles per cub. cm. Now the density ratio before and after exhaustion is y, so that 1-y is the volume of saturated emanation added. As this has passed directly and slowly over excess of phosphorus, it must be very nearly saturated, becoming diluted on mixture with the dust free air of the receiver. Hence if n, particles per cub. cm. correspond to saturation, n.(1-y)= n' =183,000; or n= 10°. There must, therefore, be at least a million nuclei per cub. cm. of the air immediately in contact with a surface of phosphorus. The value following from my electrometer work was n = 2×10o. The two methods are absolutely distinct but lead to data of the same order. It is because of the general reasonableness of the data which have followed from my simple hypothesis throughout a very wide territory of observation that I have felt bound to adhere to it, in spite of the more startling corpuscular explanations which might be adduced.

Brown University, Providence, R. I.

ART. XXXV. Klamath Mountain Section, California; by J. S. DILLER.

INTRODUCTION.

THE purpose of this general review of the sedimentary rocks of the Klamath Mountains is to render more definite the geological horizons to which a large portion of them belong, and to give their general distribution and structural relations.

A preliminary geologic map of the Klamath Mountains was issued by the U. S. Geological Survey* in 1894, upon which all the rocks below the Cretaceous were grouped under one color. Fairbanks, Smith, Anderson and Hershey have since added much to the available knowledge of the region, but excepting part of Shasta County, where fossils are abundant, the geological age of the horizons has not been definitely determined.

Last summer, accompanied by Dr. T. W. Stanton and James Storrs, the author made a trip across the southern end of the Klamath Mountains to Mad Rivert and supplemented collections made by him in that region at various times during the last decade.

The formations of the Klamath Mountains for the most part trend northwesterly in approximately parallel belts from the northern end of the Sacramento Valley to the coast between the mouth of Red Wood Creek in California and Rogue River in Oregon. It is evident that the lines of deformation which determined the trend of outcrop follow the same course and are in the main approximately parallel to those of the Sierra Nevada. These belts along the western portion of the Klamath Mountains are quite regular, but nearer the mountain center they become very irregular owing to the presence of numerous masses of igneous rocks. Most of our attention was

given to the sedimentary rocks, more or less fossiliferous, which may be grouped in the following categories: Pre-Devonian, Devonian, Carboniferous, Triassic, Jurassic, Cretaceous, Miocene, Pliocene and Pleistocene.

The pre-Devonian, Devonian and Carboniferons rocks with associated igneous masses form the bulk of the Klamath Mountains, and they occur in two belts which may be designated *Fourteenth Annual Report, plate xlv.

In this work the "Rough Geological Map of Trinity County," dated January 16, 1901, furnished in manuscript by Mr. Hershey, was found very useful. It gives a clear general idea of the areal distribution of important terranes. This map was noticed also in U. S. Geological Survey Bulletin 196, page 63. On page 9 of the same bulletin there is an outline map of the Klamath Mountains to which reference may be made for the relative position of localities mentioned in this paper.

the southwestern and northeastern. The southwestern belt embraces South Fork Mountain and all the country bordering the Salmon Mountains and Bully Choop upon the southwest, while the northeastern belt, beginning in the Bully Choop and Salmon Mountains, extends northeast to the Great Bend of Pit River. It is of importance to note that in each belt the oldest rocks lie upon the southwest, decreasing in age to the northeast, and in the northeastern belt the succession extends up through the Triassic, Jurassic and Cretaceous.

PRE-DEVONIAN.

Southwestern belt of schists.-The oldest rocks of the region are schists, of which the southwestern belt forms North Yallo Bally and South Fork Mountain and may be traced from the western part of Tehama County northwest between the South Fork of Trinity and Mad River to the coast at the mouth of Red Wood Creek, while the northeastern belt passes through Bully Choop and Salmon Mountains.

The principal rock of South Fork Mountain is a gray or greenish gray, more or less silky, mica-schist in which the mica is sericite. Although in well defined folia and fibers giving the mass a decided schistose structure, the mica is not well crystallized in distinct scales. The quartz is generally in excess of the mica and the mass is locally full of quartz veins. Another type of rock in this belt occurs in North Yallo Bally and locally along the lower portion of the southwestern slope of South Fork Mountain. The rock is greenish, generally more or less schistose, and composed chiefly of quartz and epidote. The occasional presence of blue hornblende in this rock suggests that it may be the result of contact metamorphism, but the field relations as far as known are not decisive.

The rocks bordering the schists of the South Fork Mountain upon both flanks are strongly contrasted with each other as well as with the schists. Upon the northeast are Devonian limestones, sandstones and shales cut by many igneous masses and decidedly metamorphosed. Upon the southwest between Mad River and the coast are conglomerates, sandstones and shales, at least in part of Cretaceous age. They are but little metamorphosed and are associated with comparatively few igneous rocks. The change from the schist to these rocks near Mad River is striking and indicates a profound break which may be most conveniently considered as the south western limit of the Klamath Mountains.

The general dip of the less altered sedimentary formations bordering the schists of South Fork Mountain belt upon both

*Included in the Abrams and Salmon formations of Hershey. Am. Geol., June, 1901, and manuscript map.

sides is to the northeastward and the fissile structure of the schists, although greatly crumpled, is for the most part in the same direction, suggesting that the quartz epidote schist upon the southwest side may be older than the sericite schist.

Northeastern belt of schists.-The northeastern belt of schists was seen only in the drainage of Salmon River and along Browns Creek near Douglass City on Trinity River. Although in general character the sericite schist of Brown Creek is like that of South Fork Mountain, its associations are quite different. On the west side it is limited by the belt of sediments containing the Hall City limestone, which is Carboniferous, and upon the east occurs a mass of schistose hornblende rocks apparently of igneous origin.

The South Fork Mountain belt of sericite schist is in general quite regular in outline and free from igneous masses, but the northeastern belt in Bully Choop and Salmon Mountains is much broken by a great variety of igneous intrusions.

DEVONIAN.

Southwestern Devonian belt.-In the southwestern belt there is a line of Devonian limestone lentils* which may be traced with many interruptions for over 100 miles parallel with the South Fork of Trinity River from its source to near Hoopa Valley, and throughout the whole distance the limestone rarely gets over a mile or two away from the contact with the schist of South Fork Mountain. It is probable that the same limestone occurs on the western slope of the Sacramento Valley at the Basin about 30 miles west of Red Bluff, where traces of crinoids, corals and other doubtful forms were found (1887) in one of a group of limestone ledges.

The first locality in this belt visited last summer was White Rock near the head of the South Fork of Trinity River, a few miles northwest of North Yallo Bally Mountain. The limestone is intimately associated with and broken by igneous rocks, some of which are vesicular as of surface flows. The caverned mass of limestone, which is scarcely an eighth of a mile in length, has tumbled down the slope, forming prominent cliffs and talus for nearly 1,000 feet. It is rather crystalline and the few fossils obtained were numbered 704.

Northwest from White Rock, within three-fourths of a mile, several small lenses of limestone crop out, and from one of these, only three feet in greatest extent, a number of shells and coiled forms were obtained and numbered 705. Concerning these fossils, Mr. Charles Schuchert of the U. S. National Museum at Washington, D. C., reports as follows:

* Judging from the earlier collections, this belt of limestone was doubtfully referred to the Jura-trias, U. S. Geol. Survey Bull. 196, p. 64.