Natural History. 217 



importance. We have indeed regretted that Dr. Mac Culloch 

 has so long withheld his practical information on systematic 

 geology, since we perused his work on the western isles of 

 Scotland, a work which displays attainments peculiarly fitting 

 him for the task which he has now undertaken. 



After some introductory remarks on the methods of arranging 

 rocks, which have been adopted by different mineralogists, and 

 on the plan of this arrangement and nomenclature. Dr. Mac Cul- 

 loch gives the following general catalogue of rocks, succeeded 

 by some remarks on their order of succession in nature ; 



PRIMARY CLASS. SECONDARY CLASS. 



Unstratified. Stratified. 



Granite Lowest (red) Sandstone 



Serpentine Superior Sandstones 



Stratified, Limestone 



Gneiss Shale 

 Micaceous Schist Unstratified. 



Chlorite Schist Overlying (and venous) Rocks 



Talcose Schist Pitchstone 

 Hornblende Schist occasional rocks. 



Actinolite Schist Jasper 



Quartz Rock Siliceous Schist 



Red Sandstone Chert 



Argillaceous Schist Gypsum 



Primary Limestone Conglomerate Rocks 



Compact Feldspar Veinstones 

 Appendix L 

 Volcanic Rocks. 

 Appendix II. 



Clay, Marl and Sand Alluvia 



Coal Lignite and Peat. 



Dr. Mac Culloch apologizes for the introduction of coal and 

 peat into this list; but the connexion of the former with the 

 strata in which it lies, and the important illustrations of its 

 history afforded by the latter, amply justify their insertion. 



With respect to the order of succession of the primary class, 

 the claim of granite to the lowest place is unquestioned, but after 

 it no certainty can be obtained, for the others are all found in its 

 occasional contact and in uncertain order ; to illustrate this 

 fact, the author inserts a table shewing the irregular order 

 of succession in rocks, in several parts of Britain. 



The 7th, 8th, and 9th chapters relate to the aspect and 

 structure of rocks, and in the 10th their composition is dis- 

 cussed, illustrated by a valuable catalogue of their component 

 minerals. 



■ Dr. Mac Culloch then proceeds to what we consider as a 

 highly important part of geological science, though iiitherto 



