204 



Mr. W. Bateson. 



[June 6, 



with, the granite intrusion above described, though, in the present 

 case the greater distance from the granite would make this elevation 

 a less important agent of change. 



The specimens which have been described indicate that from 

 ordinary muds and sandy silts, quartz-mica (and in some cases quartz- 

 pyroxene) rocks may be developed by contact metamorphism, and 

 that the differences now to be observed in the mineral composition 

 are due to differences in the original sediments of which the mass was 

 composed. In some cases the rock has become thoroughly crystalline, 

 in others the process is less complete, and a fair quantity of the 

 original dust, possibly in the form of kaolin, still remains. If frag- 

 ments of larger size have been present, these, though modified like the 

 matrix, can still be recognised. Some of these rocks are no less 

 crystalline than certain of the less coarsely crystalline mica- schists, 

 and occasionally exhibit a foliation. From the latter, however, they 

 can be distinguished by a practised eye. They are fair imitations of 

 some of the indubitably Archaean quartzose mica-schists, but only 

 imitations. Heat has been the main agent of metamorphism in the 

 case of the rocks just described, though probably water was present, 

 and considerable pressure may also have been exercised, which in one 

 case seems to have produced an earlier alteration. Where the original 

 constituents have differed considerably in size, a record of this 

 structure is still retained. Had the elevated temperature been 

 maintained for a longer time, molecular movements among the con- 

 stituents might have rendered this structure more indistinct, but 

 there is nothing to warrant the supposition that they could have 

 obliterated the distinction between stratulse of moderate thickness. 

 These specimens then appear to justify us in asserting a sedimentary 

 origin for certain crystalline schists (micaceous, quartzose, &c), in 

 referring their mineral bands to a stratification of the materials, and 

 in supposing their alteration due to their having been kept at a com- 

 paratively high temperature for a considerable period. 



III. " On some Variations of Cardium edule, apparently correlated 

 to the Conditions of Life." By William Bateson, M.A., 

 Fellow of St. John's College, Cambridge, and Balfour 

 Student in the University. Communicated by Adam 

 Sedgwick, F.R.S. Received May 13, 1889. 



(Abstract.) 



In 1886 and 1887 I made a journey to some of the lakes of Western 

 Central Asia for the purpose of making observations on their fauna. 

 As the waters of these lakes are of very various composition, being 

 salt, alkaline, bitter or fresh, in different degrees, I looked forward 



