218 



Carlsberg Ridge to hydrothermal processes resulting from 

 cross -faulting. Such a -suggestion is not admissible as 

 explanation of the fresh greenstone occiirrences on the 

 Mid-Atlantic Ridge; no cross-faulting is reflected in the 

 bottom topography within almost 30 min north or south 

 of their location. 



If groenstoiies similar to those from 22° N. prove to be 

 quantitatively important constituents of parts of the Mid- 

 Atlantic Ridge, interpretations of seismic, magnetic and 

 gravity data from the Ridge cannot be based on models 

 which assume the presence only of fresh basaltic rocks, 

 serpentine and unserpentinized ultramafics in a simple 

 layer-cake sequence. The probability that greenstones are 

 of general importance in the structure of the Ridge is 

 increased by our finding of greenstone fragments in the 

 coarse fraction of sediments from the western flank 

 (P.O. 22, South Pond)^ : in the specimens examined, chlorite 

 is often associated with phillipsite. Careful examination of 

 all undescribed materials from the Mid-Atlantic Ridge is 

 important in assessing the true abundance of greenstones. 

 Because of the fine-grained nature of the rocks from 22° N., 

 only petrographic inspection of thin sections or of grains, 

 combined with X-ray diffractometry, has allowed precise 

 identifications. 



Additional petrographic examinations and chemical 

 analyses are now in process, and an extended report of 

 the study will be published elsewhere. We thank Peter L. 

 Sachs and the scientific party and crew of R.V. Chain for 

 their part in the dredging, and Eugene Jarosewich for 

 making the chemical analyses. Various aspects of this 

 work were supported by the U.S. Atomic Energy Com- 

 mission (contract ^T(30-l)-2174), by the U.S. National 

 Science Foundation (grants GP921 and G'PISOQ) and by 

 the U.S. Office of Naval Research (contract 2Vonr-2196(00)), 

 at the Woods Hole Oceanographie Institution, and by 

 the U.S. Office of Naval Research under contract Nonr- 

 2216(23) with Scripps Institution of Oceanography. 



William G. Melson 

 United States National Museimi, 

 Washington, D.C. 



Vaughan T. Bowen 



Woods Hole Oceanographie Institution, 

 Woods Hole, Massachusetts. 



Tjeebd H. van Andei, 



Scripps Institution of Oceanography, 

 La Jolla, California. 



Raymond Sikveb 

 Harvard University, 

 Cambridge, Massachusetts. 



'van Andel, Tj. H., Bowen, V. T.. Sachs, P. L., and Siever, R., Science. 



148, 1214 (1965). 

 » Matthews, D. H., Vine, F. J., and Cann. J. R., Bull. Qeol. Soc. Amer., 76, 



675(1965). 

 •Turner, F. J., and Verhoogen, J., Igneous and Metamorphic Pelrology, 



534 (McGraw-Hill. New York. 1960). 

 * Hess, H. H., In Petrologic Studies: A Volume in Honor of A. F. Buddington, 



617 (Geol. Soc. Amer., New York, 1962). 



