118 FIELD GEOLOGY. 



MICROSCOPE. On the Microscopic Character of some Crystals. 

 Sorby, Quart. Jour. Geol. Soc. vol. xiv. pp. 453 

 500. 

 The Microscope in Geology. Forbes, Pop. Science 



Review, Oct. 1867. 

 On the Microscopical Structure of Eocks. Mello, 



Pop. Science Review, Jan. 1875. 

 Communications to the Geological Society. Ward, 



Rutley, and others. Quart. Jour. Geol. Soc. 

 Articles by Hull, Allport, and others in the Geo- 

 logical Magazine. 



Half-hours with the Microscope. Lankester. 

 (Hardwicke.) 



LEVELLING, &c. Civil Engineering. P.ankine. (Griffin and Co.) 

 Mathematical Instruments. Heather. (Virtue 



and Co.) 

 CHEMICAL ANALYSIS. Bischoff's Chemical Geology. 



Analysis of Soils, &c. Prof. Johnston. (Slack- 

 wood.) 

 PALEONTOLOGY. Seepage 146. 



PECULIARITIES OF STRUCTURE OBSERVABLE IN CERTAIN 

 BOCKS. 



Concretions. Within the substance of a rock en- 

 closed nodules may frequently be found, of all sizes and 

 varying in shape from flat and angular to perfectly 

 spheroidal. These are " concretions," which sometimes 

 consist of exactly the same material as the rock itself, 

 the form only of the future nodule being indicated by a 

 slight separation of the particles, or by a faint band of 

 colour. Such indications extend not o'nly as a matter 

 of course through many successive laminae of a bed, but 

 frequently (as do the fully formed concretions) through 

 two or more beds of similar character. In other cases 



