Page:Popular Science Monthly Volume 47.djvu/710

694 thousand. It is likely that some of the suggestions of the Ichnology may not be verified. It would be strange if the following thirty years of discovery should not enable paleontologists to declare positively whether the Batrachoides impressions are really the mud nests of tadpoles, or whether the "insects" are properly larval or adult hexapods, or simply Crustacea, as urged by Dana and Agassiz.

In 1857 Prof. Hitchcock accepted the appointment of State Geologist of Vermont. Though the appropriation was very small the work was energetically prosecuted, and conclusions presented in five years' time in two quarto volumes of nearly one thousand pages. Not many speculations were indulged in, though opportunity was afforded for propounding new and startling theories of the metamorphosis of rocks. The report was issued just at the time when Barrande had discharged his artillery at the opponents of the Taconic system, and compelled American paleontologists to assign the Olenellus to the primordial zone instead of the Hudson River slates. The report had been written to accord with the American view, but the authors were enabled to omit everything that did not illustrate the reference of the slates to the Cambrian terrane. The Vermont report suggested two general principles which have been of great service in the further discussion of the nature of metamorphism and the age of the New England rocks. The first point relates to the distortion and alteration of pebbles in conglomerates. As far back as 1832 Prof. Hitchcock had noticed the singular alterations in the shapes of pebbles constituting conglomerates in Rhode Island. Not till 1861 was he able to present satisfactory considerations concerning their distortion and alteration. He argued that pressure and metamorphism could totally obliterate the shapes of pebbly constituents and convert them into crystalline schists. Very few of his contemporaries followed him in this generalization. The large geological manuals of Dana and Le Conte conspicuously avoided any mention of this view. To-day the skilled petrographers of the country unanimously indorse the doctrine of the distortion and alteration of the fragmental constituents of sediments.

So long as our paleontologists referred the Cambrian fossils to the Hudson River group, their associates, as represented by Sir William E. Logan, insisted that the quartzite in western Vermont overlaid the slates, and was of Medina age. Logan also claimed a synclinal structure for the Green Mountains. Before accepting any conclusion as to their structure, Prof. Hitchcock directed that this mountain range should be carefully studied stratigraphically. A dozen sections were made at equal distances apart across the State, and it was discovered that the structure was anticlinal when not monoclinal; and hence comes the certainty