April 19, 1906] 



NA TURE 



593 



GEOLOGY IN PRACTICE.' 



T I will be sufficient to mention such names as the Black 

 ^ Hills, the Bighorn Mountains, the Foxhills and 

 Laramie Range, and the Garden of the Gods to indicate 

 thai the preliminary report on the Central Great Plains (i) 

 includes some classical and highly interesting ground. 

 The area covered by the report comprises the greater pari 

 ol South Dakota, Nebraska, and Kansas, and the eastern 

 pari of Colorado and Wyoming — an ana of no 1'ss than 

 is million square miles. 



A good deal has already been written aboul one portion 

 or another of this vast region ; the first half of Ihis volume 

 gives a clear generalised account of the stratigraphy and 

 structural geology of the whole; it is, however, by no 

 means .1 mere abridgment of previousl) gathered inform- 

 ation — it embodies the results of much original work. 



From the time when the middle-Cambrian sea washed 

 the Rockies and the adjacent highlands up to the latesl 

 physiographic conditions, the geological history ol the 

 region is here depicted in a broad manner. Oni 

 nt this country at once arrests attention, viz. the repetition 

 in one epoch after another of widespread, uniform con- 

 ditions of sedimentation — thus the greal expansi 

 Dakota-Lakota sandstone in Cretaceous times, the equally 

 widespread Arikaree sands of the 

 Tertiary, and to-day the sandy alluvial 

 deposits laid down by the rivers when 

 they can no longer bear their load, 

 and spread far and wide as the 

 streams slowly turn from course to 

 course. Less striking, perhaps, but 

 equally widespread, are the argil- 

 laceous deposits like the Pierre shale 

 of the Cretaceous. Here, as in other 

 parts of the world, a series of " Red 

 Beds " puzzles the geologist to place 

 a limit to the top of the Carboniferous 

 or the base of the Trias. 



But it is not so much for the pure 

 geolog) that this report will be read 

 as for a guide — a very practical guide 

 — to the sources of underground 

 water. I he general conditions govern- 

 ing the underground water system ol 

 1 al Plains are simple. A thick 

 succession of alternating sandy and 

 impervious sediments constitutes the 

 rocky floor of the country. These 

 beds are tilted up in the north and 

 west, and dip thence gradually south- 

 ward and eastward. Water-bearing 

 beds are found in the Cambrian and 

 in every other formation locally up to 

 the recent hills of blown sand ; but by 

 far the most important is the Dakota 



sandstone, which spreads oul as .1 greal sheel 15 -1 to 



300 feet thick beneath the entire area of the plain. This 

 sandstone is underlain by the Red Beds or by the Carbon- 

 iferous limestone and shale, or, in East Dakota, by the 

 Sioux quartzite ; it is overlain by the great mass of clays 

 and shales of the Benton, Niobrara, and Pierre form- 

 ations. The principal zone of intake lies 4000 feet to 6000 

 fei 1 abi ve sea-level on the flanks of the Rocky Mountains 

 and the Black Hills ; as a result, high pressures are found 

 in wells hundreds of miles from this region. 



In this country we trust that the bearing of geological 

 structure upon the amount and quality of water to be 

 obtained in any given area is as well understood as it is 

 across the Atlantic. Yet, although to be " like mother 

 makes it " may express the excellence of a soup, the same 

 can in no wise be said of geo-hydrological literature. We 

 have a curious shyness about graphic modes of presenting 

 information, a diffidence about making unavoidable clear, 

 so that he wdio runs may read. It is in this direction that 

 1 Reports of the United Stales Geological Survey, (i) Preliminary 

 R'port on the Geology and Underground Water Resources of tl.e Central 

 Great Plains. By N. H. Darton. 1905. (2) Preliminary Report on the 

 Geology of the Arbuckle and Wichita Mountains in Indian Territory and 

 Oklahoma. By |. A. Taff. With an Appendix on Ore Deposits by H. 

 Foster Bain. 1034- <<) The Geology of the Perry Basin in South-eastern 

 Maine. By G. O. Smith and Dayid White. 1905 



NO I903, VOL. 73] 



the volume under discussion excels; there are no fewer 

 than fourteen maps, and twelve oi these bear directly upon 

 water-supply problems. 



The landowner, the engineer, the m; Facturer, rarely 



has the time or the requisite special knowledge to sift the 

 information usually conveyed in records of well borings. 

 Ili- cannot afford to spend hours in the endeavour to dis- 

 cover whether the " ratchel " of one sinker is the " muck 

 and rubble " of another, whether " blue bungum " ran 

 really be distinguished from "hard bind," or Kimmeridge 

 clay from Gault. The geologist must know these things ; 

 whal the landowner asks him is. How deep must I sink 

 for water here? and How much may I expect to find? It 

 is true that none but Providence or the "dowser" could 

 answer these questions in terms of precise exactitude, but 

 the report before us proves how much can be done by 

 taking the subject seriously and by the application of 

 graphic methods to focus lie- geological information in its 

 varied forms into one or more simple images, so thai even 

 the " man in the street " can tnce what are the 



possibilities of any. particular situation. The maps, in 

 addition to giving tin- general geology, show also the under- 

 ground areas occupied by the more importanl formations 

 separately, ami, In means of contours, the depth of the 

 bed-rock beneath superficial deposits, tin- depth of the 



— " Toadstool Park" in badla 



Vdelia, northern Sic u 

 Brule clays 



county. Nebr. Sand- 



mosl important water-bearing stratum, ami the altitude of 

 tin- head (if water, as well .1-. other useful information. 



The volume is profusely and beautifully illustrated. 

 Three .,1 the plates, exhibiting forms produced by erosion, 

 have lii-i-n reproduced in accompany this rn 



Mr. Taff in hi- reporl (2) describes the structure and 

 stratigraphy of the two groups of hills, the Arbuckle 

 ami Wichita Mountains, which rise abruptly, like islands, 

 from the Red Rock plain in Oklahoma and Indian Terri- 

 tory, a region which lies south-easl oi thai described in 

 the previous report. 



These two hill-groups have a common alignment, their 

 axes trending north-westward and south-eastward. Their 

 geological history appears 10 be identical: underlying the 

 sedimentary rocks in each ease are pre-Cambrian granites, 

 granite-porphyries, anil aporhyolite: — the eldest rock is a 

 galil.ro, in the Wichita -cup. The succeeding Cambrian 

 and Ordovician strata bear no evidence of folding: the 

 period ol uplift which has led to the exposure of the 

 igneous pre-Cambrian rocks began in the middle of the 

 Pennsylvanian (Carboniferous) epoch and culminated near 

 its closi , lull re the deposition of the Red Rocks (? Carbon- 

 iferous or Permian) which in this region constitute the 

 prevailing surface nil. 



\\ 1 are glad to see that the field staff records its appreci- 



