Russell Institution, 469 



latter source, is evident; for although the plain and shore 

 are covered with fragments, these consist almost entirely of 

 the primary rocks : and besides the pieces of the wall 

 which have not felt the fire, there are angular fragments, 

 showing pretty clearly that tliey were not collecttd on an 

 alluvial plain, but broken irom the rocks where they are 

 found. 



Dr. M. next proceeds to describe the various states in 

 which the different stimcs are found. 



The puddinsstone exhibits the greatest variety of 

 changes. It is found in every state, from a black glass to 

 a spunky scoria capable of floating in water, sometimes ex- 

 hibitin<r the gradual succession of changes from incipient 

 calcination to complete fusion. To ascertain the degree of 

 heat necessary to produce the corresponding changes in this 

 rock. Dr. M. submitted various pans of it to the furnace, 

 and found that some of the fused substances must have been 

 brought to that state in a heat not less than 100^ of 

 Wedgwood's scale ; a heat at which many varieties of 

 eartlien-ware are baked. 



Dr. M. next gives a short account of the vitrified fort of 

 Craig Fhadric in Invernessshire, and of another in Gallo- 

 way ; in both of which, but more particularly in the 

 former, he observed circumstances quite analogous to what 

 he had already found at Dun MacSniochain ; and the con- 

 clusion he has been led to form is, that the vitrification of 

 these forts is the effect of desitrn. 



The Society adjourned till November. 



RUSSELL INSTITUTION. 



May. — In the fourth Lecture Mr. Bakevvell proceeded to 

 describe the stratified rocks containing rock-salt and coal. 

 The coal districts in England and in other parts of the 

 world, he said, were generally separated from the compact 

 limestone which contains metallic veins, by thick beds of 

 coarse gi it-stone and sand- stone, in which some vegetable 

 remains first make their appearance. In the midland 

 counties of England, there are two kinds of rock interposed 

 between tlie coal and the liuie, forming together a mass of 

 three hundred yards in thickness. The lower bed consists of 

 a dark reddish-brown shale, in which strata of micaceous 

 sand-stone and beds of dark limestone occasionally occur. 

 The upper rock was called by Mr. Wiiitchurst mill-stone 

 grit, from its containitig beds of hard siliceous grit-stone, 

 wsed for mill-stones. This rock varies both in colour and 



quality 



