470 JOURNAL OF THE WASHINGTON ACADKMY OF SCIENCES VOL. 11, NO. 19 



The igneous rocks of the District have been but little studied, 

 but there is reason to believe that the igneous complex is more femic 

 toward the borders through magmatic differentiation. The analyses 

 indicate a close comagmatic relationship between the various rocks. 

 Further study of the igneous rocks of the District is very desirable. 



ABvSTRACTS 



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. — Geology of the igneous rocks of Essex County, Massachusetts. 

 Charles H. Clapp. U. S. Geol. Survey Bull. 704. Pp. 132. 1921. 



Essex County is the northeasternmost county of Massachusetts. The 

 special area whose geology is more particularly discussed in this bulletin 

 lies almost wholly in the southern part of the county. Geologically the 

 area is well known, chiefly because of its alkaline igneous rocks, among 

 which are the types essexite and bostonite. Besides presenting local problems 

 the area illustrates certain general features of the geology of igneous rocks, 

 the more important of which are: (1) The sequence of the volcanic, batho- 

 lithic, and dike phases of an igneous cycle. (2) The differentiation of two 

 contrasted groups of rocks, the sub-alkaline, or calci-alkalic, and the alkaline. 

 (3) The origin of shatter breccias along molar contacts of batholiths and the 

 slope of molar contacts. (4) The contact assimilation of country rock by 

 invading igneous magmas, forming hybrid rocks. (5) The formation of 

 diabase dikes contemporaneously with irruptions of alkaline granitic rocks. 



The writer throws light on some of the broader principles of the geology 

 of igneous rocks, notably the formation of hybrid rocks by contact breccia- 

 tion and assimilation and by impregnation of invaded rocks, and the differ- 

 entiation of subalkaline magmas. The report discusses in detail the litho- 

 logic character, alteration, contact and structural relations of the consider- 

 able variety of igneous rocks found in the region. R. W. Stone. 



G'EOhOQY .—Permian salt deposits of the sottth-central United States. N. H. 

 Darton. U. S. Geol. vSurvey Bull. 715-M. Pp. 19 (205 to 223), pi. 1 

 ^ (21), figs. 10. 1921. 



The bulletin presents a review of knowledge about the area of underground 

 salt in eastern New Mexico, the Panhandle of Texas, and adjacent parts 

 of Oklahoma and Kansas. A map shows the probable approximate extent 

 of the area which is at least 650 miles long and 150 to 250 miles wide. Infor- 

 mation about the salt beds is derived from drilling for oil, gas, and water, 

 but the difficulty of recognizing salt when penetrated in the ordinary methods 

 of drilling is pointed out. The salt succession undoubtedly occurs in the 

 Permian beds known as the Manzano group in New Mexico and the Marian 

 formation in Kansas associated with red beds, gypsum, anhydrite, dolomite, 

 and limestone. The salt is not a continuous body, but probably composed 

 of separate lenses and the sections in which it occurs in different places are 

 not comparable in detail. 



The deposit lies in a wide synclinal basin with minor folds. The thick- 

 est salt is approximately at the bottom of the basin. This basin may there- 



