BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 

 VOL. 33, PP. 353-370 JUNE 30, 1922 



WEIGHT OF SEDIMENTARY ROCKS PER UNIT VOLUME » 



BY ALFRED C. LANE 



{Presented before the Society December 29, 1921) 



CONTENTS 



Page 



General importance of the data 353 



General engineering data on porous and f ragmental rocks 354 



Methods of determining weight per unit volume 356 



Work of Charles C. Moore '. 359 



Data from drill cores 361 



Data on friable material 362 



New data from tests on glacial brick-clays 363 



Comparative data on other clays 366 



Applications to gravitative anomalies 367 



Summary 369 



General Importance of the Data 



The importance of the study of the volume, composition, and weight 

 of rocks was the theme of the presidential address of C. C. Moore 2 before 

 the Liverpool Geological Society. 



The specific weight of a rock, as ordinarily given in textbooks or de- 

 termined by chemists, is not the weight of the rock, but the weight of the 

 rock powder. In a rock there are always pores, which may be filled with 

 air, gas, oil, or water, and thus it is only in the compact rocks, like granite, 

 where the porosity is very low, that the two expressions, "sp. gr." and 

 "weight of rock per unit volume," accompanying chemical analyses, are 

 nearly equivalent, if the latter is given in tons (metric) per cubic meter. 

 I use these units in tables, but in the text, to avoid decimals, I refer to 

 thousands of ounces per cubic foot, assuming that a thousand ounces of 

 pure water have the volume of one cubic foot. In such expressions the 

 figures for weight per volume are directly comparable with specific grav- 



1 Manuscript received by the Secretary of the Society March 6, 1922. 

 This paper is one of a series composing a symposium on isostasy. 



2 Proceedings, vol. ix, part 1, pp. 129 et seq. ; part 3, p. 247. See, also, February, 1S9S. 



XXIII— Bull. Geol. Soc. Am., Vol. 33, 1921 (353) 



