H. Woodward — Anthrapalcemon from M. Coal-measures. 361 



maintain the pressure, then the metamorphic action will not take 

 place and a granite or dolerite may come to rest against a slate 

 without showing the least sign of alteration at the contact. 



The purpose of this note, however, is not to discuss the whole 

 subject of metamorphism but to draw attention to the want of 

 definitiveness in the terms used by authors in describing the 

 metamorphic rocks. It seems to me to be impossible to attain any 

 definitiveness unless we use molecular energy as a basis : the mischief 

 of this is that it makes it necessary for geologists to add to their 

 already overburdened subject the additional trouble of physical 

 chemistry. 



Addendum. — Since writing the above I have received Eecherches 

 sur V exhalaison volcanique, by A. Brun, in which it is recorded that 

 certain of the metamorphic minerals, kyanite, epidote, vesuvianite, 

 etc., have their crystalline structure destroyed at temperatures in 

 many cases much below the fusion - point. Epidote, for instance, 

 loses its crystalline structure at 900° C. and fuses at 1250° C. 



Epidote = 2 H Ca CA1 Fe) 3 Si 3 13 , molecular volume 296 



Anorthite = 3 Ca Al" 3 Si 3 8 ,, ,,303-3 



So that, in spite of its having within its molecular structure water, 

 iron, and a surplus of lime, epidote has a far smaller bulk than the 

 igneous mineral anorthite. The destruction of the crystalline structure 

 by heat long before fusion seems to point, therefore, to expansion of 

 the molecule. All the metamorphic minerals do not show this 

 character, garnet and spinel for instance, but the presence in a rock 

 of one mineral that does might be taken as an indication that the 

 rock belongs to the metamorphic class. 



YI. — On a large form of Anthrapalcemon from the Clay- 

 ironstone Nodules of the Middle Coal-measures, Sparth 

 Bottoms, Rochdale. 



By Henry Woodward, LL.D., F.R.S. 

 A S long ago as 1836 Prestwich published his historical paper 

 j~\_ "On the Geology of Coalbrook Dale", 1 and in it he figured 

 a Crustacean carapace under the name of Apus dubuis. 



In 1861 2 J. "W. Salter figured and described some new Coal-measure 

 forms of Crustacea which he referred to the genus Anthrapalcemon, 

 gen. nov., and included therein Prestwich's Apus dubuis. 



In my second year's Presidential Address to the Geological Society, 

 in 1896, I dealt with the "Life-history of the Crustacea in Later 

 Palaeozoic and in Neozoic Times ", and, under the Decapoda 

 Macrura, I referred to those of the Coal-measures (Proc. Quart. 

 Journ. Geol. Soc, 1896, vol. lii). "Eight species of Anthrapalcemon 

 from the Coal-measures of Scotland and England, one from Illinois, 

 U.S.A., and one from Nova Scotia, illustrate the abundance of these 

 small Crustacea in the Carboniferous period. They have many points 

 in common, but probably deserve more than specific differentiation. 



1 See Trans. Geol. Soc, 1840, vol. v. 



2 See Quart. Journ. Geol. Soc, vol. xvii, p. 530, 1861. 



