The distribution of the New Hampshire formations was made out for the most part before any assistance was derived from the labors of Dr. G. W. Hawes and other petrographers. Twenty years ago, at the date of the final publication of the New Hampshire maps, the doctrine of an igneous origin of the crystalline schist had hardly been hinted at. What seems elemental to the modern petrographer who has acquired his technical education since 1890 was unknown then, and the classification given in the report may not agree with that now taught. In the midst of the diverse views entertained, Professor Hitchcock classified the rocks of northern New England according to this principle: rocks that are identical in petrographical composition are assumed to have had the same origin, and to be synchronous. Professor Hitchcock was almost the first of American geologists to employ the petrographer as a help to the understanding of the crystallines--as was evident by the very valuable contributions to knowledge in Part IV of the New Hampshire Report as prepared by Dr. Hawes. A vexing question concerning what are now called Cambrian terranes divided geologists for a quarter of a century after 1857, and had to be considered in preparing the geology of Vermont in 1861. This was the Taconic controversy. Trilobites had been discovered in Vermont, which were misunderstood by most of the American geologists following Hall, Logan, Dana, and others. In giving the species the technical name first of _Barrandesi_ and then _Olenellus_, Prof. James Hall asserted its derivation from the Hudson River group--relying upon the stratigraphical determinations of Sir W. E. Logan. As soon as Barrandes's attention was called to these trilobites and the attendant publication, he wrote his famous letter to Logan in 1860, declaring that there must be a mistake somewhere. That error was discovered in time to be eliminated from the Vermont report of the following year. Professor Hitchcock had charge of the field work in this Cambrian district, and his views of the arrangement of the formations are in agreement with those of the latest workers in the field. He applied the term of _Georgia_ to one division of the terrane in 1860; and the designation has been generally adopted since that time. Jules Marcou claimed priority in the suggestion of the application of the term, but upon the publication of Professor Hitchcock's statement on the subject the credit of priority was awarded to him by Director Walcott, of the United States Geological Survey.