TO GEOLOGICAL KESEARCH. 69 



character, except that the forms of organic life give evidence of a 

 different age, whilst in those portions which exhibit the " roe- 

 stone " arrangement, from which the rock derives its name, as in 

 some Bath and Portland stones, it is found, by the microscopical 

 examination of transparent sections, that each rounded concretion 

 is composed of a series of concentric spheres, enclosing a central 

 nucleus, which nucleus is often a Foraminiferal shell. 



The application of the microscope to geology is not, however, 

 limited to the determination or discovery of organic structure ; 

 very important information may be obtained by its means respect- 

 ing the mineral composition of rocks and the mode of their 

 formation, and it is specially in the study of the Eruptive rocks 

 that this method of observation is most valuable. Very little 

 comparatively had been done in England on this subject till quite 

 a recent period, when Messrs. Sorby, Allport, and others turned 

 their attention to it, and did some most valuable work in micro- 

 scopic geology. 



In 1858, Mr. Sorby brought out his celebrated paper on the 

 " Microscopic Structure of Crystals " in the Quarterly Journal of 

 the Geological Society^ in which he describes the glass, stone, and 

 gas or vapour cavities in the minerals of the pitchstones of Arran, 

 the lavas of Vesuvius, and some of the basaltic rocks of Scotland, 

 as well as in the quartz of granites, and thence draws conclusions 

 respecting the common origin of these rocks. 



In 1867, an article appeared upon the " Microscope in Geo- 

 logy " in the Popular Science Review^ written by Mr. David Forbes. 

 The author draws attention to Mr. Sorby's discoveries, and shows 

 how the different minerals in volcanic rocks may be distinguished 

 from each other by means of the microscope, and gives figures 

 illustrating the microscopic structure of various rocks. 



The first of a series of valuable papers by Mr. Allport 

 appeared in 1869 in the Geological Magazine, describing the basalt 

 of South Staffordshire, and others followed on the " Basaltic 

 Rocks of the Midland Coal-Fields," " The Microscopical Examina- 

 tion of Rocks and Minerals," etc. etc., the author arriving at the 

 conclusion that there is no essential difference between the 

 eruptive rocks of different geological epochs. 



A very complete account of the rocks of the Lake district of 



