[18]. Warren, G. K., Preliminary report of explorations in Nebraska and Dakota, this Journal, 27, 380, 1859.

[19]. Lesley, J. P., Observations on the Appalachian region of southern Virginia, this Journal, 34, review, 413–415, 1862.

[17]. Conrad, T. A., Notes on American geology, this Journal, 35, 237–251, 1839.

[20]. Dana, J. D., On denudation in the Pacific, this Journal, 9, 48–62, 1850.

——, On the degradation of the rocks of New South Wales and formation of valleys, this Journal, 9, 289–294, 1850.

[21]. Hubbard, O. P., On the condition of trap dikes in New Hampshire an evidence and measure of erosion, this Journal, 9, 158–171, 1850.

[22]. Hayden, F. V., Some remarks in regard to the period of elevation of the Rocky Mountains, this Journal, 33, 305–313, 1862.

[23]. Newberry, J. S., Colorado River of the West, this Journal, 33, review, 387–403, 1862.

[24]. Jukes, J. B., Address to the Geological Section of the British Association at Cambridge, Quart. Jour. Geol. Soc., 18, 1862, this Journal, 34, 439, 1862.

[25]. Powell, J. W., Exploration of the Colorado River of the West, 1875. For Powell’s preliminary article see this Journal, 5, 456–465, 1873.