abstracts: geology 117 



GEOLOGY. —Apishapa, Colo., Folio. George W. Stose. Folio No. 



186, Geologic Atlas of the United States, U. S. Geological Survey. 



January, 1913. Topographic, geologic, and structure maps, and 



sheet of illustrations. 

 The Apishapa quadrangle is one-quarter of a square degree situated 

 20 miles southeast of Pueblo, Colorado. It was geologically surveyed 

 by G. K. Gilbert and his assistants some years ago and was recently 

 completed and revised by G. W. Stose. The topography of the quad- 

 rangle is tjTDical of the semiarid Great Plains region, comprising rolling 

 treeless plains, low mesas, and deep rocky canyons. An old dissected 

 peneplain, drainage modifications, and other physiographic features are 

 discussed and figured. The rocks exposed are all of Cretaceous age 

 except the oldest rocks observed in some of the deeper canyons — the 

 Morrison formation of possibly Jurassic age — and the surficial gravels 

 of Tertiary and Quaternary age. Lower Cretaceous rocks are recog- 

 nized and mapped for the first time in this vicinity as the Purgatoire 

 formation. The structure of the quadrangle is a sharp dome-like up- 

 lift centering in the Rattlesnake Buttes, with a total vertical displace- 

 ment of 2500 feet in the quadrangle. The hard Dakota sandstone 

 forms the land surface over a large portion of the higher part of the 

 dome. Numerous normal faults occur on the flanks of the uplift, and 

 the resulting intricate displacements are brought out on the geologic 

 structure map by deformation contours. A sharp local dome structure 

 is regarded as probably the result of the intrusion of a laccolithic body 

 of igneous rock emanating from the source of the Spanish Peak intru- 

 sion 25 miles to the southwest. These igneous rock are represented 

 in the quadrangle by scattered dikes of rather unusual composition. 

 The petrographic description of these is contributed by Whitman Cross. 



G. \V. S. 



GEOLOGY. — Geology of the salt and gypsum deposits of southwestern 

 Virginia. George W. Stose. Bulletin 530 (separate N), U. S. 

 Geological Survey. Pp. 14^37. 1912. 

 The salt and gj^psum deposits are in the vicinity of Saltville, Va., 

 and occur in red and gray clays of Mississippian ("Lower Carbonifer- 

 ous") age adjacent to the Rome fault, a great fault thrusting Cambrian 

 dolomite and limestone upon the Carboniferous strata. A section is 

 given of the lower Carboniferous rocks in the syncline adjacent to the 

 fault, comprising the Price sandstone, at the base, Maccrady ("Pulaski") 

 formation, and the Newman limestone, and the equivalence of the 



