final determination regarding any proposed change from the geological order of these strata known at present should be postponed until the extensive paleontological material from this region, especially from the Agate Spring Quarry, is studied.

At this point I wish to record my idea regarding the origin of the sediment in this fossil quarry and its immediate neighborhood, to

FIG. 4. Cliff one mile north of Agate Spring Fossil Quarry. The light-colored stratum is laminated.

gether with the probable way in which the bones may have been deposited. I have said that the stratum in which the fossils are found in the quarry is of a light color. In fact this layer is easily distinguished by its color from the under- and over-lying strata in this locality. The stratum varies in thickness from a few feet to approximately twenty feet, which is the maximum vertical depth. I have examined

this particular layer in different places, sometimes at one or two miles distant from the quarry, and have nearly always found abundant evidence of laminated structure. It would appear from the evidence at hand that this light-colored stratum is of lacustrine origin. The color precludes the idea that there was heavy vegetation, which, according

to the views of the writer, would have imparted a darker hue to the stratum. This supposed lake probably had a small geographical area, and judging from the comparatively thin, light-colored stratum, a relatively short duration in geological time.

I referred to a hard sandstone stratum forming the floor of the quarry. In this stratum are often found foot-bones and sometimes fragments of limb-bones, which are almost unrecognizable on account of their much worn condition. It is evident that the bones were subject to moving water. Bones of greater weight and those which have broad surfaces are always quite perfect in this stratum, retaining all their sharp angularities. It would seem that there are at least two plausible explanations of these facts.

(1) That there might have been a stream of water which gradually carried the foot bones of Moropus and other animals down stream, thus causing their worn condition. (2) That the supposed lake, referred to above, might have had coves along its borders, especially at the mouth of streams. There might have been a large spring of water at one of these particular recesses near the shore of the lake, which was much resorted to by various animals during certain seasons of the year. When the water of the lake rose as the result of swollen streams and continuous rains, it might have reached this veritable bone-yard. The bones, which were small and had angles offering less resistance to the waves, might then have been washed back and forth by the action of the water, while flat and heavier bones remained stationary. This latter view is, I think, the more plausible, according to the evidence at hand in the Agate Spring Fossil Quarry and its immediate neighborhood.

XIX. DESCRIPTION OF TWO NEW BIRDS FROM

BRITISH EAST AFRICA.

BY HARRY C. OBERHOLser.

Among the birds from Mombasa, British East Africa, collected by Mr. William Doherty, and recently acquired by the Carnegie Museum,' are specimens of two forms which appear to be unnamed. Through the courtesy of Dr. W. J. Holland the following descriptions of these are here presented.

Astur tachiro orienticola, subsp. nov.

Subspecific characters. Similar to Astur tachiro tachiro, but rather smaller; upper parts lighter, the head and cervix conspicuously paler than the remaining upper parts, the sides of head and neck much lighter still; posterior lower surface paler, with much less of rufous, particularly on flanks and flags.

Description. -Type, adult male, No. 7763, Carnegie Museum; Mombasa, British East Africa, September or October, 1900; William Doherty. Pileum and cervix slate-gray, the remaining upper surface slate color, posteriorly with a slight brownish tinge; tail sepia-brown, the outer feathers lighter and rather more rufescent, all the rectrices tipped with buffy white and crossed by four broad blackish bands, and most of them, including the middle pair, with two or three white or whitish spots in the light interspaces of the inner webs; wing-quills fuscous, the basal portions of inner webs white, the inner webs of all but tertials and innermost secondaries barred with blackish or dark brown; sides of head and neck grayish plumbeous; under surface white, posteriorly washed with buff, the chin and upper throat vermiculated with pale grayish, the crissum sparingly and narrowly barred with the same; the rest of the ventral surface including flags conspicuously, regularly, and rather closely, though narrowly, barred with wood-brown, this becoming more rufescent on the sides of the body, where also the bars are wider, and paler and on the lower abdomen where they are narrower and farther apart; lining of wing creamy 1 Cf. Holland, ANNALS CARNEGIE MUSEUM, III., 1905, pp. 453-463.

white, with scattered and irregular barrings of dull brown. Length of wing, 198; tail, 172; exposed culmen with cere, 22; culmen without cere, 16.5; tarsus, 59; middle toe, 33; middle claw, 12.5; hind claw, 18 mm.

The considerable differences which separate this race from true Astur tachiro have already been indicated by Dr. Reichenow." Its range includes probably at least the eastern, or coastal, portion of both. British and German East Africa. The original Astur tachiro3 came from southern Africa, as did also the Nisus polyzonus of Lesson,* so that the present form seems hitherto to have received no name.

Cisticola heterophrys, sp. nov.

Specific characters. Similar to Cisticola chiniana, but lacking any well-defined superciliary stripe; upper surface duller and much more uniform, the pileum darker and without trace of dusky streaks, the feathers of back and wings without conspicuously light edges, lower surface not so purely white, and laterally more shaded with grayish.

Description. Type, adult male, No. 8125, Carnegie Museum; Mombasa, British East Africa, September or October, 1900; William Doherty. Pileum uniform rufescent mummy-brown; remainder of upper surface hair-brown, somewhat rufescent on the cervix, the feathers mostly with darker centers which on back and scapulars produce a streaked effect; tail bistre-brown, indistinctly and narrowly barred with dusky; the middle pair of rectrices with a wider subterminal bar of dark brown, the remaining feathers with a broad terminal bar of buff and a subterminal one of black; wings fuscous, the greater, lesser, and median coverts, together with the tertials, edged rather broadly with hair-brown, the greater coverts more rufescent, the primary coverts, primaries, and secondaries margined with chestnut and rufous chestnut; lores and orbital ring dull buff; sides of head dull light brown mixed with buff; sides of neck hair-brown; ventral surface dull white, slightly washed with buffy, the sides of breast and body shaded with gray; thighs rufous; lining of wing buffy white; bill black, the base of mandible whitish.

2 Vögel Afrikas, I, 1901, p. 552.

3 Falco tachiro Daudin, Traité d'Ornith., II, 1800, p. 90 ("pays d'Auteniquoi"). 4 Nisus polyzonus Lesson, Traité d'Ornith., 1831, p. 58 (Cape of Good Hope).