Oil the Htractun of Glaciers. 171 



the ensuing summer. Sir John Herschel's actinometer gave a value 

 of the solar radiation nearly independent of its position upon snow 

 or rock. 



April 18.— The Right Hon. Lord Gheenock, V. P. in the 

 Chair. 



1. On the Structure, Formation, and Movement of Glaciers ; 

 and the probable cause of their former extension and 

 subsequent disappearance. By James Stark, M.D., 

 F.R.S E. 



The author endeavoured to prove, from the recorded facts stated 

 by different writers, that the crystalline particles of which the ice 

 of glaciers is composed, do not sensibly enlarge after being consoli- 

 dated into compact ice ; that the crystals have been shewn to be 

 fully and perfectly formed in the course of a few nights in the 

 Polar Regions ; and that they have a position perpendicular to the 

 layer of ice which they form, — their length being thus determined 

 by the thickness of that layer. 



The author next considered the different forms of stratification 

 met with in glacier?, and stated that the greatest confusion prevailed 

 on this point, different forms of stratification being confounded to- 

 gether. He therefore considers glaciers as composed of — 



1. Horizontal Strata, or layers lying in tlie position in which 

 they were first deposited, and only seen in the upper regions of the 

 mountains. He stated that these strata were usually regarded as 

 marking the additions which the icy mass had annually received, 

 each layer being the accumulated snow of one year ; but that, as 

 the Meteorological Tables kept at the Hospice of the Great St Ber- 

 nard shewed that from 300 to 700 inches of snow fell during the 

 six winter months, it seemed possible that each layer marked the 

 separate storms of snow ; or, if they marked the annual accumula- 

 tions, they apparently proved, what had not previously been sus- 

 pected, that snow and ice waste nearly as rapidly in the upper as 

 they do in the lower regions. 



2. Vertiral aii'l Lon/jituJinal Strata. The author statud, that 

 these strata were always of great tenuity, were more oi- less perpen- 

 dicular, but had always a direction parallel with the retaining wall 

 or length of the glacier. Their mode of formation he attributed to 



