abstracts; geology 237 



Other things being equal, the extent and character of erosion varies 

 with the bed-rock. The nature of the rock determines the character 



of the soil and this determines the kind and rate of erosion. 



A. H. Brook-v 



GEOBOGY.— Geologic Atlas of the United States. Folio No. 177. 



Bargettstoivn-Carnegie folio, Penn. E. W. Shaw and M. J. Munn. 



U. S. Geological Survey. Pp. 11, with maps and sections. 1911. 



Oil and gas fields of the Carnegie Quadrangle, Penn. M. J. Munn. 



Bulletin U. S. Geological Survey No. 156. Pp. 99, with maps 



and sections. 

 The outcropping rocks belong to the Conemaugh, Monongahela, 

 and Greene formations of the Carboniferous system and consist of shale, 

 sandstone, and limestone with minor amounts of coal and clay. Beneath 

 the surface are similar rocks of Allegheny, Pottsville, and Pocono age, 

 and even older rocks have been reached by the drill. The beds dip 

 gently south but the structure is modified by minor irregularities. 



Almost all the coal produced is taken from a bed known as Pittsburg 

 coal. This coal outcrops extensively, but in general it is below the 

 surface in the southern half of the district and up near the tops of the 

 hills in the northern half. A few feet above this coal is another bed 

 three or four feet thick known as the Pittsburg rider which is mined to 

 some extent. The oil and gas are found in sandstones 1000 to 2000 

 feet below the surface, belonging mostly in the Pottsville and Pocono 

 formations. 



Two surface features of especial interest are: (1) heavily gravel- 

 covered terraces in the larger valleys of the region lying 200 to 300 feet 

 above present streams and (2) a symmetry in the minor drainage lines 

 of the region, the small tributaries flowing southeast being much longer 

 than those flowing in an opposite direction. E. W. S. 



GEOLOGY. — Geology and underground waters of southern Minnesota. 

 C. W. Hall. E. O. Meinzer, and M. L. Fuller. Water-Supply 

 Paper U. S. Geological Survey No. 256. Pp. 406, with maps and 

 sections. 1911. 

 The region here described includes approximately the southern two- 

 fifths of the State of Minnesota and has an area of 28,265 square miles. 

 Five great rock divisions occur in southern Minnesota. In the order 

 of age, these are the Archean, Algonkian, Paleozoic (here including the 

 Cambrian, Ordovician, and Devonian systems), Cretaceous, and Qua- 

 ternary. Tertiary stream deposits doubtless exisl in <ome localii 



