B. M. Beeleii—The Viscosity of Ice. 265 



The first and third of these seem undoubtedly to be represented on 

 the mainland by the older limestones and Manzanilla Series 

 respectively, and thus in the main Nicoya must be regarded as 

 a westward extension of the coastal belt of the mainland, and not as 

 has sometimes been hinted at, as a fragment of some older land mass. 

 The extensive area of flat ground round the villages of Nicoya and 

 La Colonia, which is again seen further to the north, I regard as 

 a prolongation of the raised peneplain which forms the country 

 between Manzanilla and Avangares on the mainland. With regard 

 to the igneous rocks, thej^ undoubtedly belong to an entirely 

 diflPerent province from those of the rest of Costa Rica, with the possible 

 exception of the Manzanilla limburgite and the monzonites of the 

 Cerro Candelaria, both of which are more closely related to the 

 Nicoyan series of teschenites than to the pyroxene andesites of 

 the mainland. As regards the age of these alkaline rocks, I am 

 inclined for the present to regard them as intrusive into the 

 older limestones or sediments belonging to the same group, but 

 the relationship of the different rocks is, I suspect, much complicated 

 by faulted junctions. 



V. — The Vjscosity of Ice. 

 By E. M. Deeley, M.Inst.C.E., F.G.S. 



WITH a view to showing that distortion under stress may take 

 place in ice when several degrees below the freezing-point, 

 Dr. Main ^ made a number of experiments at St. Moritz in the 

 Engadine during the winter of 1887. Although, as Main says, 

 "The experiments are to be regarded rather as proving the existence 

 of continuous extension under tensile stress than as determining its 

 amount," the records of his tests are sufiiciently detailed to admit of 

 the viscosity being calculated. 



The tests were all made with the temperature below the freezing- 

 point. He recorded the temperatures at the time extension I'eadings 

 were taken, and in some instances states the range of temperature 

 between observations ; but his records do not enable the true mean 

 temperature to be ascertained, for during the nights the temperatures 

 were lower than during the days. On this account the I'esults cannot, 

 except in a somewhat rough manner, be used to ascertain the variation 

 of viscosity with temperature. 



These experiments are of particular interest as Kelvin - used them 

 in a paper read before the Geological Society of Glasgow in 1888. 

 He says: "Main's experiments gave perfectly definite results though 

 difliering considerably with temperature." Adopting a viscosity 

 obtained from Main's experiments, Kelvin comes to certain conclusions 

 Avith regard to the possible thickness of floating ice fed by snow 

 falling upon it, and also the probable thickness of an ice-sheet on land 



1 Proc. Eoy. See, vol. xlii, p. 491, 1887. 



" Popxdar Lectures and Addresses, vol. ii, p. 319. 



