318 



Prof. T. G. Bonney. On the 



[May 5, 



radial slit being as near as possible to the point of reappearance, the 

 whole field was crowded with bright lines, fifty or more being visible 

 in the short space between wave-length 5600 and b. I noticed no 

 difference in the length of these lines. Clouds and rain soon put an 

 end to all chance of further observations. 



Interesting sketches were made during totality of the outer 

 streamers by Captain Masterman and Mr. Osborn, of H.M.S. 

 " Bullfrog," who both used the circular disks arranged so as to cover 

 the brighter portions of the inner corona. The instantaneous view 

 that I obtained of the corona, most exquisitely defined on the white 

 cap of the spectroscope, and the rapid glance I took with an excellent 

 I inocular, confirm the positions of the two principal rays drawn by 

 Captain Masterman, but I observed at the same time a shorter ray 

 between the two, which appears otherwise to have escaped detection, 

 and I noticed the leaf-shaped. curvature of the ray in the north-west. 



The darkness was never much less than that of a fair moonlight 

 night. 



II. "Note on the Microscopic Structure of Rock Specimens 

 from three Peaks in the Caucasus." By T. G. Bonne y, 

 D.Sc, LL.D., F.R.S.. Professor of Geology in University 

 College, London. Received April 5, 1887. 



Although our knowledge of the petrology of the Caucasus has been 

 considerably augmented of late years through the labours of Abich, 

 Favre, Tschermak, and others, so much ground still remains un- 

 trodden among its mountain peaks that hardly any specimen can be 

 entirely without interest. Those described in the present note have 

 come from the following localities: — (1) The summit of Tau Tetnuld; 

 (2) rocks from the upper part of Guluku ; (3) the summit of Elbruz. 



The specimens from Tau Tetnuld and Guluku were collected by 

 Mr. W. F. Donkin, during his expedition in company with Mr. 

 Clinton Dent in the summer of 1886, and to the former I am indebted 

 for the following note on the localities. 



" Tau Tetnuld is one of the peaks of the central Caucasian chain, 

 in the great Koschtan-Tau group which lies about midway between 

 Elbruz to the N.W., and Kasbek to the E.S.E. Prom Koschtan-Tau 

 the main ridge forming the watershed runs somewhat north of west, 

 dropping gradually in height; but for some three or four miles 

 forming a magnificent wall on the northern side, covered with a 

 succession of steep snow-slopes and hanging glaciers. A long portion 

 of this ridge, including three more or less well-marked elevations, is 

 called Djanga; the next elevation on the ridge — a much more obvious 

 one, forming indeed a symmetrical snow pyramid — is Tau Tetnuld. 



