72 Scientific Intelligence. 



pp. 151-182, plate 35. — The author has made a careful study of 

 the data now obtainable in regard to the various channels around 

 the Manhattan Island, with a view to deciding as to their proba- 

 ble origin. In 1881 the subject was discussed by J. D. Dana* 

 and their formation ascribed to the presence of belts of limestone 

 whose erosion was believed to explain the topographic features. 

 Hobbs, however, concludes that there is no sufficient evidence of 

 a correspondence between the directions of belts of limestone, or 

 dolomite, and those of the various channels; on the contrary, he 

 regards them as owing their origin to lines of jointing and dis- 

 placement. The account of Julien is appealed to, giving the 

 location and orientation of the principal dikes on the island, 

 which quite generally run along the direction of the avenues. 

 Julien shows that the orientation of the drainage has been largely 

 determined by the planes of fracture. Julien has also shown 

 that, besides these, there is a system of cross faults nearly at 

 right angles to the avenues, or, in other words, along the cross 

 streets. Thus the fissure planes occupied by the dikes, and the 

 perpendicular series often occupied by quartz lenses and pegma- 

 tite, both correspond very closely in their direction with the two 

 series making up the main drainage system. The observations 

 of the author also show that many of the most prominent joint- 

 planes in the rocks of the island have the direction of the cross 

 fissures, N60°W. He concludes that "the role of the dolomite 

 in fixing the locations of the present channels would thus appear 

 to have been a subordinate one, excepting in so far as the direc- 

 tion of its boundaries has been determined by its fissure planes." 



4. The Isomorphism and Thermal Properties of the Feld- 

 spars. Part I, Thermal Study ; by Arthur L. Day and E. T. 

 Allen, pp. 13-75. Part II, Optical Study; by J. P. Iddings, 

 pp. 17-95. Plates i to xxvi. With an introduction by George 

 F. Becker, pp. 4-12. Publication No. 31 of the Carnegie 

 Institution of Washington. — The first part of this volume gives 

 the complete presentation of the results obtained by Day and 

 Allen in their very important work upon the thermal relations of 

 the feldspars. This is accompanied by a series of twenty-six 

 beautiful plates illustrating the crystallization of the various 

 compounds and the effect of very high temperatures upon them. 

 An extended abstract of this paper has already been given in the 

 number of this Journal for February, 1905 (pp. 93-142). 



Part II gives the results of an optical study by Iddings of the 

 series of lime-soda feldspars synthetically obtained by crystalli- 

 zation in open crucibles from fused constituents. In addition to 

 the detailed description of thin sections of the individual com- 

 pounds, a general summary is given which contains some points 

 of so' much importance in petrography that we quote largely 

 from it: 



" The results of these synthetical experiments agree closely in 

 some respects while differing in others. They agree in general 



* This Journal, xxi, 25, 443; xxii, 313, 1881. 



