Notices of Memoirs — The Geological Survey. 363 



accompany the specimens in the museums. It is in contemplation 

 also to emplo}"^ photography for duplication of the six-inch field-maps. 

 Besides the geological Memoirs, the Survey has published a series 

 of Decades of British organic remains, with plates and descriptions, 

 also Monographs of important genera or groups of fossils, including 

 Professor Huxley's essays on Pterygotus, the Belemnitidge, and the 

 crocodiles of Elgin, and Mr. Newton's memoirs on Cretaceous fishes 

 and Pliocene vertebrates. 



3. Peteogkaphical Wokk. — In the earlier days of the Geological 

 Survey each member of the staff determined for himself, by such 

 tests as he could apply, the various rock;s encountered by him in 

 the field. Only in rare cases were chemical analyses made for him. 

 The study of rocks had fallen into neglect in this country, being 

 eclipsed by the greater attraction of the study of fossils. The intro- 

 duction of the microscope into geological investigation has, however, 

 changed this apathy into active interest. It is now recognized that 

 apart fi'om mere questions of nomenclature, I'ocks contain materials 

 for the solution of some of the most important problems in phj'sical 

 geology. Accordingly, microscopic inquiry has in recent years been 

 organized as one of the branches of the Geological Survey, and now 

 aifords constant and material aid in the progress of the mapping, 

 three members of the staff being specially detailed for petrographical 

 ■work in the office and in the field. Chemical analyses are likewise 

 made, so as to afford all available information as to the composition 

 of the mineral masses encountered in the field. 



The original specimens from which the thin slides have been 

 prepared are kept in cabinets, so that if any accident should befall 

 a slide, a new slice can at once be cut. The mounted slides are 

 arranged in separate cabinets. A large number of such slides has 

 now been accumulated. From Scotland alone nearly 8,000 have 

 been determined, and are ready for reference at any moment. 



But besides assisting the field-work, the petrographers are engaged 

 in determinations required for the arrangement of rock-specimens 

 in the museums at Jermyn Street, Edinburgh, and Dublin. The 

 collectors emploj'^ed under the supervision of the surveying officers 

 to make illustrative series of specimens of the rocks of each district, 

 send these up to the office for examination and for insertion in the 

 museum. In the course of the research thus imposed on them, the 

 petrographers are from time to time enabled to make important 

 original contributions to petrographical science. Moreover, by con- 

 ferring in the field with the officers who are engaged in mapping, 

 they are enabled to realize the nature of the problems to be dealt 

 with by the surveyor, and the points on which petrographical 

 assistance is needed. Their determinations are embodied in the 

 Memoirs on the geology of the several districts. 



4. Pal^ontological Work. — In a country where the geological 

 formations are to a large extent fossiliferous, it is necessary to pay 

 close attention to the organic remains found in the rocks, to collect 

 specimens of them, to determine these specifically, and to regulate 

 thereby the geological boundary -lines upuu the maps. The duty of 



