42 i On some Unknown Comlinations of [Dec. 



5. Beds of granular lime-stone in granite, gneiss, mica-slate, 

 and clay-slate, are sometimes intermixed with these rocks at their 

 line of junction, or pass by almost imperceptible gradations into 

 them, particularly into the gneiss, mica-slate, and clay-slate. 



6. Beds of granite in grey-wacke are either distinctly separated 

 from it at their meeting, or they are much intermixed : and it 

 frequently happens that there is a beautiful and distinct transition 

 from the granite into the grey-wacke. 



7- Beds of flinty-slate frequently occur in clay-slate : sometimes 

 the two rocks are distinctly separated ; sometimes they are inter- 

 mixed at their junction ; and in other instances we observe the 

 clay-slate becoming gradually more silicious, and at length passing 

 into the flinty-slate. 



8. Beds ox granular quartz or sand-stone occur in clay-slate : 

 these beds in general are separated from the slate at their junction ; 

 but instances occur where they are intermixed, and also where the 

 slate becomes gradually more silicious, and at length passes into 

 the sand-stone. 



9. Beds of amygdaloid, sometimes of vast magnitude, occur in 

 the old red sand-stone formation ; the amygdaloid is occasionally 

 intermixed with the sand-stone where they meet, or there is a 

 gradual transition from the one rock into the other. 



10. Beds of trap tuff occur in the old red sand-stone and coal 

 formations : these, like the beds of amygdaloid already mentioned, 

 are either distinctly separated from the bounding rock, or they are 

 intermixed with it, or gradually pass into it. 



11. Green-stone occurs frequently in beds in the old red sand- 

 stone and coal formations, and exhibits precisely the same relations 

 as the amygdaloid, trap tuff, &c. 



Article IV. 



On some Unknown Combinations of Chromic Acid with different 

 Bases.* By Frofessor John. 



I undertook these experiments with a view of filling up some 

 gaps which still exist in the table of chromates; but I must acknow- 

 ledge thai < ] \e? do not possess the accuracy which might have been 

 obtain- ,i by performing the experiments upon a larger scale. When 

 we attempt to crystallize ^ahs in small quantities we have often to 

 struggle with- insurmountable difficulties; and even in the most 

 favourable circumstances, it is very difficult to determine the state 

 of small, and often imperfectly formed, crystals. 



* Translated from Sclrwrfgger'a Jfeuea Journal fur Chemie unJ PbysiSc, iii. 3'S. 



