310 Notices respeclhig New Booka. 



as iar;;e as those of coarse primitive limestone. The next state 

 is t^acrchariae, then fine grained and arenaceous ; a compact va- 

 riety Iiaving a porL-elianeous aspect and bhieish-grav colour suc- 

 ceeds; this towards the outer edge heconies yellowish white, and 

 insensibly graduates into tlie unaltered chalk. The flints in 

 the altered chalk usually assume a gray yellowish colour: the 

 altered chalk is highly idiosphorcscent when subjected to heat. 

 In the neighbourhood of* Glenarin, where a singular compound 

 dyke, consisting of three branches, traverses the chalk, the in- 

 cluded masses have been changed into granular marble. Other 

 instances of this change of the chalk are ijuoted, as also of 

 changes effected by the whin dykes on rocks which they traverse, 

 as of red ^sandstone to hornstone, of the slate clay o/ the coal- 

 measures to flinty slate, and of the coal itself to cinders. The 

 inference which Mr. Conybeare would draw from these facts, 

 " were it allowable to speculate on subjects so remote from ac- 

 tiial observation," is, " that the hypothesis which ascribes the 

 formation of the floetz-trap rocks to submarine volcanoes, which 

 were active at a very remote period before the seas and continents 

 had assumed their present relative level, is both in itself more 

 consistent, and in its application to the actual phaenomena more 

 satisfactory than any other. 



Professor Hailstone's paper and Mr. Aikin's, though both 

 short, will prove interesting to geologists. Dr. MacCulloch's 

 on the Geology f'f Glen Tilt presents several facts deserving of 

 much attention respecting stratification and the necessity of di- 

 stinguishing more precisely than has hitherto been done, the 

 different species of rocks. But our limits prevent our giving 

 more particulars respecting these papers : Mr. Horner's on the 

 Geology of Somersetshire, and others in this interesting volume. 



^ Practical Essay on Chemical Reagents or Tests; ilb/strated 

 ly a Series of Experiments. By Fredrick Accum, Operative 

 Chemist, &c. &;c. pp. 26.". By Callow, Crown-court, Soho. 

 When it was ascertained that many of the substances of na- 

 ture are compounds of different principle':, methods were suc- 

 cessfully employed to separate those principles by chemical 

 means ; and the name of Reagents or Tests was given to those 

 substances by means of which their analysis was accomplished. 



To those who study chemistry, whether from motives of pro- 

 fit, amusement, or general iMforniation, a knowledge of the action 

 of chemical tests is absolutely necessary; indeed it constitutes 

 one of the first objects to which the attention of the chemist 

 ought to be directed. The practical application of chemical 

 tests requires comparatively but little skiil^ and no costly ap- 

 paratus 



