652 • ABSTRACTS 



istic of the locality. These peculiarities are mentioned under the 

 detailed descriptions of the different localities which follow the more 

 general portion of the paper. Mr. Ries' investigation of the relation 

 between the optical and chemical properties of the pyroxenes, shows 

 that the extinction angle does not increase with the percentage of FeO, 

 thus disagreeing with Wiik's results, although the latter himself found 

 several exceptions to his rule. Comparing the extinction angle with the 

 corresponding sums of the ferrous and ferric iron gives no better results. 

 If, however, the combined percentages of FeO, Fe.^Og and Al.^Og be 

 taken, a more regular series is obtained. If, furthermore, those con- 

 taining less than 3 per cent, of AlgOg be excluded from the list as 

 more properly belonging to Diopside, a still better series is obtained, 

 though not even then is the series a perfectly regular one. The results 

 of etching agree very closely with those obtained by Wulfing and by 

 Greim. In the chemical investigation Mr. Ries has attempted to cal- 

 culate in each case the mixture of metasilicates. His analyses indicate 

 that Tschermak's theory of the relation between AlgOg and the oxides 

 of Ca, Mg, and Fe holds good in the case of only about one-half of 

 the New York pyroxenes analyzed. Not the least valuable portion of 

 the paper is a list of the literature bearing on the subject and including 

 some sixty papers. H. F. B. 



Fifteenth Annual Report of the United States Geological Survey, i8gj-4. 



The administrative portion of the report is followed by five papers 

 of considerable importance. The first is a preliminary report upon 

 the Geology of the Common Roads of the United States, by N. S. 

 Shaler, and includes an outline of the history of American road build- 

 ing, with studies on the value and distribution of road stones, the 

 methods of their use, the effects of geologic structure on the grade of 

 roads, the value of block paving and paving brick and the action of 

 rain and frost upon roads and road material. The paper is a timely 

 contribution to a subject of increasing interest. 



The second paper is by L. F. Ward and is upon the Potomac 

 formation. It is the result of detailed studies upon the flora and 

 the stratigraphy of the formation. It is notable in that Mr. Ward 

 divides the formation into six separate series of beds to which local 

 names are given. 



K. C. Lawson contributes a sketch of the Geology of the San 



i 



