PETROLOGICAL ABSTRACTS AND REVIEWS 579 



Noble, L. F. "Contributions to the Geology of the Grand Canyon, 

 Arizona, The Geology of the Shinumo Area, (continued), Part 

 II," Am. Jour, of Sci., iv ser., XXIX (1910), pp. 497-528. PI. i. 



The writer gives a detailed description of the stratigraphy and lithology 

 of the Unkar (Algonkian) rocks of the area. The sedimentary rocks 

 consist mostly of alternating shales and quartzitic sandstones with some 

 slate and considerable thicknesses of limestone. 



The diabase intrusions described are of special interest. A sill of from 

 650 to 950 feet in thickness is intruded above one of the limestone members. 

 Below this intrusive occurred large amounts of serpentine in bands and 

 nodules. These show no trace of an alteration structure which might 

 indicate a derivation from pyroxene, hornblende, or olivine. This fact 

 and the fact that serpentine and asbestos are not developed within the 

 diabase itself lead the author to believe that they are the result of contact 

 metamorphism, conditioned by the invasion of the limestone by the diabase. 

 The diabase itself consists primarily of plagioclase feldspar (near labra- 

 dorite) and olivine in about equal amounts, with a subordinate quantity of 

 augite and brown biotite. Ophitic intergrowths of augite and plagioclase 

 occur throughout, and pegmatite dikes cut the mass. 



At one point the rock at its upper contact is a pink hornblende syenite 

 which appears to grade downward into the normal diabase. Transition 

 specimens were not collected and the author's suggestion that the syenite 

 is due to differentiation in place is only tentative. 



A map showing the distribution of Algonkian rocks in the Grand 

 Canyon region is appended. 



Albert D. Brokaw 



Parsons, A. L. "Ein neues Sklerometer," Zeil. Kryst., XL VII, 

 (1910), 363-70. Figs. 2. 

 Describes a new instrument for measuring hardness, giving the con- 

 struction and adjustments of the instrument and a few comparative results. 



W. T. SCHALLER 



Ransome, F. L. " Notes on Some Mining Districts in Humboldt 



County, Nevada," Bull. U.S. Geol. Survey No. 414. Pp. 71. 



1909. 



These notes are based upon reconnaissance work. With the exception 



of a small portion, the field had been previously geologically mapped by the 



Fortieth Parallel Survey. In general, the granites described as Archean 



by that survey are intrusives in Mesozoic rocks; many of their Triassic 



