REVIEWS 599 



taken up, and the development of the present streams in the portion west of the Mis- 

 souri. These streams are thought to have made their way eastward to the James 

 River valley, and several other peculiarities of drainage are mentioned. In the early 

 Pleistocene the streams are represented as flowing over the same channels as in the 

 Pliocene, for it is thought that the Kansan ice-sheet did not occupy the James River 

 valley. During the later Pleistocene the James River valley was filled and the pres- 

 ent course of the Missouri River is thought to have been inaugurated. 



IOWA. 



Calvin, Samuel. Geology of Page County, low^a Geol. Survey, Vol. XI, 



pp. 398-460, 1 90 1. 



The topography is characterized as an eroded drift plain, and the erosion is con- 

 sidered much more mature than in southeastern Iowa on the Kansan drift. The 

 question is raised whether this drift may not be pre-Kansan. The valleys are par- 

 tially graded up by a somewhat pebbly silt of loess-like aspect, and this grading up 

 took place after the valleys reached their present large dimensions. Attention is 

 called to a pebbly bed which occurs on the higher parts of the slopes at the base of 

 the loess, which is thought to be the result of the removal of the fine parts of the sur- 

 face of the till sheet and a resulting concentrating of pebbles. The statement that 

 no such pebbly bed occurs in eastern Iowa is too broad, for the reviewer has noted it 

 at the junction of the loess with the underlying Illinoian till sheet. (See Journal 

 OF Geology, Vol. VI, p. 181.) 



Calvin, Samuel. Concerning the Occicrrence of Gold and So7ne Other 

 Mineral Products in Iowa. Am. Geol., Vol. XXVII, pp. 363-72, igoi. 

 It is shown to be a fallacy that the topography of Iowa throws light upon the 

 occurrence of valuable minerals deep in the earth. The presence of gold in the 

 glacial deposits is also no indication of gold in the underlying rocks, since it has 

 been derived from areas of crystalline rocks far to the north. It is also noted that 

 gas, such as occurs in drift deposits near Herndon and Letts, is not to be taken as 

 indication of larger amounts in underlying rock strata, for it appears to be formed 

 from vegetation included in the drift. 



Calvin, Samuel, Concrete Examples from the Topography of Howard 

 County, Iowa. Am. Geol., Vol. XXX, pp. 375-81, Pis. 27, 1902. 

 Descriptions and photographic views are given of the Loess-Kansan drift area, 

 the loess margin, and the lowan drift plain. The Loess-Kansan area presents a 

 mature type of erosional topography, while the lowan drift plain is very slightly 

 eroded. The erosion contrasts are in line with other evidence, such as weathering 

 and oxidation, in showing that the Kansan drift is many times older than the lowan 

 drift, or than its own coating of loess. It is considered a conservative estimate to 

 give the Kansan drift an age fifty times as great as the lowan. 



Farnsworth, p. J. Wheft Was the Mississippi Valley Formed? Am. 



Geol., Vol. XXVIII, pp. 393-96, 1901. 



The present stream is in process of re-excavating a very old valley, whose floor 

 was cut to a level more than 100 feet below the low water level of the river. The 

 erosion is thought to have begun far back in Paleozoic times. 



