ABSTRACTS 



Authors of scientific papers are requested to see that abstracts, preferably 

 prepared and signed by themselves, are forwarded promptly to the editors. 

 The abstracts should conform in length and general style to those appearing in 

 this issue. 



GEOLOGY. — Two lamprophyre dikes near Santaquin and Mount 

 Nebo, Utah. G. F. Loughlin. U. S. Geol. Survey Prof. Paper 

 I20-E. pp. 9. 1918. 

 There is no local evidence by which these lamprophyre dikes can 

 be correlated with other igneous rocks. It is assumed that they repre- 

 sent a late stage of the Tertiary volcanic period. The dike rocks are 

 dark gray to black, dense, and porphyritic. Biotite is the only con- 

 spicuous megascopic mineral, and constitutes about 20 per cent of 

 the rock. The northern dike has a glassy groundmass crowded with 

 phenocrysts of augite, biotite, olivine, and magnetite, and minute 

 crystals of apatite. The southern dike consists of phenocrysts of biotite, 

 augite, apatite, and magnetite in a groundmass of feldspar. The chem- 

 ical composition of the northern dike is shown by analysis and com- 

 pared with rocks of similar composition. The rock is classed as a 

 vitrophyric albite minette. It seems probable that the two minettes 

 discussed are genetically related to a monzonitic magma represented 

 by the latite breccias and flows of the region. R. W. Stone. 



GEOLOGY. — New graphic method for determining the depth and thick- 

 ness of strata and the projection 0} dip. Harold S. Palmer. U. 

 S. Geol. Siu-vey Prof. Paper 120-G. Pp. 7. with 3 plates and 5 

 figures. 191 8. 

 This paper presents three charts by means of which rapid solution 

 of the following problems may be made, namely: (i) to find the depth 

 to a stratum, given the dip and distance from the outcrop; (2) to find 

 the thickness of a bed or series of beds, given the dip and the distance 

 across the outcrop ; and (3) to find the inclination of the trace of a plane 

 upon a second plane, given the dip of the first plane and the angle 

 between the strike of the two planes. 



Simple directions for the use of the charts are followed by a discussion 

 of the principles and accuracy of the method. H. S. P. 



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