Time with slow and measured tread moving over the buried records of the past—Time, upon whose ample store the geologist is wont to draw with an unsparing hand, seems to have accelerated his pace in this nineteenth century, and hurries onward as if his few remaining sands were well-nigh run.

Agassiz, after describing the intermaxillary bone of Megalichthys, makes the following brief statement regarding the fossil which is the subject of the present paper: “M. König possède une pièce detachée qui parait etre le même os.”

The accompanying analytical Table of the genera of the Rhabdophora which are especially treated of in the present paper is here offered as a first and suggestive sketch for an improved arrangement of these forms. The foregoing conclusions have been employed in its construction, and are embodied in the general scheme.

In accordance with our plan, we now proceed to sketch the history of the Lower Palæozoic rocks in North America. While European geologists were carrying out the researches which have been described in the first and second parts of this paper, American investigators were not idle. The geological studies of Eaton led the way to a systematic survey of the State of New York, the results of which have been the basis of most of the subsequent geological work in eastern North America, and which was begun by legislative enactment in 1836.