Page:The Habitat of the Eurypterida.djvu/16

 middle part of the Belt Terrane in Montana. The remains are very numerous, most of them being exceedingly thin films flattened in a calcareous shale and showing no definite surface markings (288, 21). Weller has collected specimens from the Altyn limestone at the type locality north of Altyn in the valley of Swift Current Creek, Montana, at the base of the Appekunny Mountains where the remains are embedded in a fine calcarenyte matrix and show surface markings (288, 40, pl. 7, fig. 4). Specimens have also been collected from the Altyn limestone at about the same horizon near Johnson Creek on The Continental Divide, Alberta, Canada. These show surface markings, and have been referred by Walcott to B. danai (288, 40, pl. 7, figs. 2, 2a, 3).

In a recent communication from Dr. Walcott, I have his statement about the occurrence of the merostome remains in the different sections. In the southeastern area of the Big Belt Mountains he found a series of sandy shales and sandstones between the top of the Newland limestone and the base of the Greyson; these carried Beltina. In the sections in the Little Belt Mountains Walcott found it difficult to determine whether the shales carrying Beltina belonged to the Greyson or to the Newland. In the Northern Montana section the merostome remains are found in the lower portion of the Altyn limestone, so that, concludes Walcott, "the correlation on the basis of fossil evidence is that the Greyson and Altyn are about the same age." The fossils from the Altyn limestone were identified by Walcott as Beltina danai, and Clarke and Ruedemann agree that the fragments are remains of merostomes. They are, however, skeptical about the correlation of the Altyn with the Belt terrane and they are justified in this skepticism so long as the correlation is based upon the fossils alone, for if the organic remains in the Belt terrane are not eurypterids and are not the same as those in the Altyn, then the correlation is unfounded. Furthermore, the palaeontological evidence alone would not be sufficient for correlation, and, if, as I believe, these Pre-Cambric formations are to be regarded as of continental origin, then neither physical nor faunal data will lead to correlations, since the same lithological successions will be repeated time and again in different localities and in addition the synchroneity of river faunas is difficult to establish.

Thus at present it is impossible to say which authority is to be accepted. Walcott plans to do more work on these sections in the