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barrancas on the same coast, wrote: “The sections were carefully studied in each locality, but since we require here only an illustration . . . it will suffice to describe a characteristic relation observed in the Barrancas del Norte, north of Mar del Plata. . . . The upper surface of the basal formation in the Barrancas del Norte [the Chapadmalalan] is eroded and the hollows are filled by later deposits, sometimes of one character, sometimes of another. It will be seen that the formation was carved by an agent that undercut the sides and rounded the bottoms of the hollows, leaving masses with sharp points or edges in relief. Wind produces these effects in this material, whereas water cuts channels having nearly vertical walls. Thus it would appear that wind erosion is favored. . . . The phenomenon recurs . . . in other exposures of the formation at Miramar” (Hrdlicka 1912, pp. 22–23). Romero thought the same hollows to be the result of marine action and mountain building rather than wind.

Then regarding the stone layer itself, found in the hollows, Willis wrote: “The pebbles . . . could have been formed only by wind action, since the loess of which they consist would readily melt down in water and lose its form. The formation thus suggests arid conditions” (Hrdlicka 1912, p. 24). Willis, a member of the U.S. Geological Survey, was an expert in the study of loess formations, having conducted extensive investigations in the course of geological expeditions in North America and China.

Romero’s qualifications are unknown to us, and his view that the pebbles are a sign of marine action seems in great disharmony with the geological evidence. The same is true of his assertion that the Chapadmalalan at Miramar is actually a fairly recent marine mud deposited against the base of the cliff. This opinion was based upon visual inspection of a piece of sediment from an excavation at Miramar. Romero (1918, p. 31), stated about this chunk: “It is constituted principally of a mixture of clayey elements and sand, very fine, and is deposited uniformly in layers about 1 mm thick, which indicates successive, slow, tranquil deposition in a bay. Throughout the piece are many holes .25–1.0 mm in diameter, forming small tunnels in the direction of the plane of stratification, and on close observation you can see traces of organic remains of annelids.” On the strength of this one piece of sediment, which he did not demonstrate to be typical of the entire deposit, Romero (1918, p. 31) then concluded: “It is obvious the bed was deposited on the sea bottom, and any animal bones or human artifacts found in the beds were brought there by the action of waves or were washed down from the cliff and covered up.” Romero neglect to mention that annelids include not only marine worms but ordinary earthworms.

Furthermore, Willis described the formation at the base of the cliffs as follows: “At Miramar . . . the formation . . . consists of loess-like alluvium, the surface of which has been eroded and filled in by wind” (Hrdlicka 1912, p. 27). Describing the Chapadmalalan layer in the Barrancas del Norte, which he regarded as continuous with that at Miramar, Willis wrote: “The writer is inclined to regard this formation and similar deposits as due to river work on confluent flood plains” (Hrdlicka 1912, p. 23). A river flood plain is generally covered with water during only a small part of the year, and not every year. Such conditions are very favorable for fossilization of animal remains in primary position, especially when conditions are becoming more arid. At such times, animal remains may be buried during floods and remain undisturbed for long periods of time because of lower water levels. In short, Willis gave no hint that the deposit at the base of the cliff at the Miramar site was a recent marine formation.

The incorrectness of Romero’s interpretation of the stratigraphy at Miramar is confirmed by modern researchers, who identify the formation at the base of the cliff as Chapadmalalan and assign it to the Late Pliocene, making it 2–3 million years