386 ' EXPEKIMENT STATION RECOED. 



In the application of tlie results of these tests to the correlation of the phys- 

 ical properties of the rock families with their mineral components the following 

 conclusions have been reached: 



"(1) Igneous and metamorphic roclis, owing to a higher degree of crystalliza- 

 tion and a preponderance of silicate minerals, offer a greater resistance to 

 abrasion than nearly all varieties of sedimentary rocks. 



"(2) The coarse-grained intrusive rocks of the igneous class are harder, but 

 break more readily under impact than the finer-grained volcanic varieties of like 

 mineral composition. 



"(3) The deleterious effect of atmospheric weathering on the wearing qual- 

 ities of rocks has been demonstrated. 



"(4) The cementing value of rocks is, to a certain degree, measured by the 

 abundance of secondary minerals resulting from rock decay. 



"(5) Metamorphic rocks have, as a rule, a low binding power, owing to a 

 regeneration of secondary minerals and to the effects of heat and pressure. The 

 foliated types part readily along planes of schistosity, and therefore are not 

 well adapted to I'oad construction. 



"(6) The quantitative mineral analysis of rocks serves to a certain extent 

 as a measure of their useful properties for i-oad construction." 



The construction of macadam roads, A. B. Fletcher ([7. 8. Dept. Agr., 

 Office Pub. Roads Bui. 29, pp. 56, pis. 6, figs. 10). — This bulletin describes in 

 some detail the best practice in macadam road construction, and especially that 

 followed by the Massachusetts highway commission. 



" It is intended as a brief description and discussion of the several processes 

 and essential features entering into the construction of macadam roads in rural 

 sections. Some data as to costs, especially for the information of road officials 

 who have not undertaken such work, are included. 



" The details of construction may require modification to some extent to be 

 suitable for different parts of the country, depending upon amount of rainfall, 

 temperature, and topography, but the general type of road to which this bulletin 

 relates is adaptable to nearly all parts of the United States where suitable 

 stone exists or to which such stone may be carried without excessive cost." 



Corn-harvesting machinery, C. J. Zintheo {U. S. Dept. Agr., Fai-mers' Bill. 

 303, pp. 32, figs. 20).— This is a condensation of Bulletin IT."^ of this Office 

 (E. S. R., 18. p. 785). 



Farm buildings, {Chicago, 1907, rev. ed., pp. 310, pi. 1, figs. 515). — This is 

 a new and thoroughly revised edition of this book, and consists of " a compila- 

 tion of plans for general farm barns, cattle barns, dairy barns, horse barns, 

 sheep folds, swine pens, poultry houses, silos, feeding racks, sheds, farm gates, 

 portable fences, etc., all representing construction in actual use." 



Ventilation, heating, and lighting, W. H. Maxwell {London, 1907, 2. ed., 

 rev. and oil, pp. yi + 151: rcr. in \afure [London], 76 {1907), No. 1968, p. 

 26S). — "The simple principles and practice of ventilation, heating, and lighting 

 are described in this volume from the point of view of the sanitary engineer." 



RURAL ECONOMICS. 



West Virginia agriculture and its possibilities, J. B. Garvin et al. {Rpt. 

 W. Va. Bd. Agr., 1907, No. 6, pp. //S, figs. 18, maps -J).— As a means of fur- 

 nishing information to prospective agricultural settlers, this bulletin describes 

 the topography of the State, including descriptions of its natural and mineral 

 resources, the origin and distribution of its soils, and the crops grown thereon. 

 The live-stock industry of the State is also described. 



It is claimed that there are 5.ir)5.5o2 acres of virgin land, or about P>0 per cent 

 of the total area of the State, which are capable of being brought under cultiva- 



