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After the turn of the century, Walcott moved his field work northward along the spine of the Rocky Mountains, focusing first in the Lewis Range of northwestern Montana, from which he reported diverse stromatolitelike structures (Walcott, 1906) and, later, chains of minute cell-like bodies he identified as fossil bacteria (Walcott, 1915). His studies in the Canadian Rockies, from 1907 to 1925, were even more rewarding, resulting in discovery of an amazingly well-preserved assemblage of Cambrian algae and marine invertebrates—the famous Burgess Shale Fauna that to this day remains among the finest and most complete samples of Cambrian life known to science (Walcott, 1911; Gould, 1989).

Walcott's contributions are legendary—he was the first discoverer in Precambrian rocks of Cryptozoon stromatolites, of cellularly preserved algal plankton (Chuaria), and of possible fossil bacteria, all capped by his pioneering investigations of the benchmark Burgess Shale fossils. The acknowledged founder of Precambrian paleobiology (Schopf, 1970), Walcott was first to show, nearly a century ago and contrary to accepted wisdom, that a substantial fossil record of Precambrian life actually exists.

A. C. Seward and the Cryptozoon Controversy

The rising tide in the development of the field brought on by Walcott 's discoveries was not yet ready to give way to a flood. Precambrian fossils continued to be regarded as suspect, a view no doubt bolstered by Dawson's Eozoon debacle but justified almost as easily by the scrappy nature of the available evidence. Foremost among the critics was Albert Charles Seward (1863–1941), Professor of Botany at the University of Cambridge and the most widely known and influential paleobotanist of his generation. Because practically all claimed Precambrian fossils fell within the purview of paleobotany—whether supposed to be algal, like Cryptozoon stromatolites, or even bacterial—Seward's opinion had special impact.

In 1931, in Plant Life Through the Ages, the paleobotanical text used worldwide, Seward assessed the “algal” (that is, cyanobacterial) origin of Cryptozoon as follows: “The general belief among American geologists and several European authors in the organic origin of Cryptozoon is . . . not justified by the facts. [Cyanobacteria] or similar primitive algae may have flourished in Pre-Cambrian seas and inland lakes; but to regard these hypothetical plants as the creators of reefs of Cryptozoon and allied structures is to make a demand upon imagination inconsistent with Wordsworth's definition of that quality as ‘reason in its most exalted mood' ” (Seward, 1931, pp. 86–87).

Seward was even more categorical in his rejection of Walcott's report of fossil bacteria: “It is claimed that sections of a Pre-Cambrian limestone



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