694 THE POPULAR SCIENCE MONTHLY. 



thousand. It is likely that some of the suggestions of the Ichnol- 

 ogy 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 oppor- 

 tunity 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 con- 

 glomerates in Rhode Island. Not till 1861 was he able to present 

 satisfactory considerations concerning their distortion and altera- 

 tion. 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 in- 

 dorse the doctrine of the distortion and alteration of the frag- 

 mental 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 stratigraph- 

 ically. 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 



