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formations beneath is not known. The contact between the formation and the overlying Marathon limestone is not a sharp one and is further complicated by local folding. In some places a thin conglomerate appears to form the base of the overlying formation and rests on shales assigned to the Cambrian. Elsewhere the basal beds of the Marathon formation are thin limestone flags containing Dictyonema.

In 1915 Baker and Bowman collected fossils from two anticlinal mountains 8 to 12 miles southwest of the town of Marathon-one locality 6 miles northeast of the junction of Peña Colorada and Maravillas Creeks, on East Bourland Mountain (pl. 6, B), and the other 1½ miles northeast of the creek junction, on Simpson Springs Mountain (pl. 5, E). The higher fossil collections from both places came from the Maravillas chert, but below this fossils were found in nodular masses of dense or crystalline gray limestone, in part glauconitic, embedded in clay shales and brown sandy flagstones. The base of the lower series was not exposed. In collections from both localities Ulrich distinguished an Upper Cambrian fauna "like * * * that found in the Dunderberg shale of the Nevada * * * section", and in addition, at the second place, a fauna characterized by Symphysurina, to be correlated with "a well-marked zone in the lower part of the Pogonip of Nevada" of which "the evidence permits of only one conclusion * * * namely, that it is Ozarkian, and most probably Upper Ozarkian." On the basis of these determinations, Baker and Bowman set off the lowest beds at the Simpson Springs Mountain locality as the ‡ Brewster formation, of Upper Cambrian age, named for Brewster County. The similar clays and flagstones lying above them, containing the so-called "Ozarkian" fossils, they considered to be member 1 of their ‡ Marathon series. The direct superposition of Maravillas (Upper Ordovician) on supposed Ozarkian of Ulrich at this place and the absence of the intervening Ordovician zones of other localities were explained by a marked erosional unconformity at the base of the upper formation.

Recent collecting at these localities has disclosed some puzzling anomalies not explained by the first interpretations. The sandy flagstones and the matrix of many of the thin layers of conglomerate are profusely fossiliferous at different levels below, between, and above the limestone "nodules." The flagstone fossils are largely species of Diplograptus, Climacograptus, and Glossograptus, and the conglomerate fossils are various bryozoans, brachiopods, trilobites, and crinoids. In the surrounding region these fossils characterize the Woods Hollow shale, of Middle Ordovician age. In addition, from the shales F. A. Bush and B. H. Harlton have obtained a microfauna which they state is of Black River age. Furthermore, southwest of Garden Springs the Woods Hollow shale, here plainly overlying the earlier Ordovician, also contains large "nodules" of the mottled and glauconitic limestone. Additional collecting from the "nodules" of Simpson Springs and East Bourland Mountains has given plentiful evidence that the fossils are of Cambrian and early Ordovician age.

It is here suggested that the "nodules" are in fact large erratic boulders of Cambrian and Ordovician limestones embedded in the shaly and flaggy strata of the Middle Ordovician Woods Hollow shale. As it is clear that the type locality of the ‡ Brewster formation is a part of the Woods Hollow shale, it has been recommended that the name " ‡ Brewster" should be abandoned. The name "Dagger Flat sandstone" is used here for the indigenous Cambrian strata.

Two faunas appear to be represented in the boulders of the Woods Hollow shale. The oldest of these is of Upper Cambrian age. In a collection made by C. L. Baker on East Bourland Mountain E. O. Ulrich has identified the following species:

• Lingulella manticula (White).
• Lingulella desiderata (Walcott).
• Acrotreta idahoensis (Walcott).
• Acrotreta sp.
• Alokistocra aff. A. aoris (Walcott).

In a collection by the writer on Simpson Springs Mountain Ulrich has recognized Agnostus and several new species of Upper Cambrian trilobites. Ulrich notes that the first three species in the list from East Bourland Mountain are typical Upper Cambrian fossils which have been found in Nevada and elsewhere, and that the fauna is decidedly like that found in the Dunderberg shale of the Nevada Upper Cambrian section.

Baker, C. L., and Bowman, W. F., op. cit. (Texas Univ. Bull. 1753), p. 83.

Communication to the writer, 1931. Van der Gracht, in referring to the Dagger Flat sandstone (op. cit., table Vb), makes the following comment: "There is controversy whether the Cambrian is represented at Marathon. The above version is contested by B. H. Harlton and F. A. Bush, who advised the writer that the type locality yielded a profusive microfauna of Black River age." The collections of Bush and Harlton came from the type locality of the ‡ Brewster and not of the Dagger Flat formation.

King, P. B , Pre-Carboniferous stratigraphy of the Marathon uplift: Am. Assoc. Petroleum Geologists Bull., vol. 15, p. 1064, 1931.