GEOLOGY. 229 



bowlders exist in gneiss. The theories as to the original method of 

 accumulation of gneisses would be modified by this demonstration. 

 There still remains, however, too much diversity of opinion concerning 

 what constitutes a gneiss. It is generally known that a purely eruptive 

 granite can assume a stratified structure, and many waiters are not clear 

 enough in dividing such stratified granites from the group of crystalline 

 schists. Little progress will be made till this is done. A gneiss with 

 bowlders might be a stratified granite, and granites are liable enough 

 to include strange rocks. 



One writer has even urged that gneisses are tuff rocks. He recalls 

 that the moon's surface, upon which water has not worked, is entirely 

 covered with eruptive rocks and volcanic products, and argues there- 

 from that our oldest rocks must have been volcanic. No one knows, 

 however, what were our oldest rocks, and it is generally supposed that 

 the primitive rocks were early and finally buried beneath their own 

 sediments. 



In the mean time Lehmann, Heim, Baltzer, and still others have con- 

 tributed to our knowledge of the mechanical distortion, the softening 

 and recrystallizing of pebbles and solid rock masses by geological agen- 

 cies. 



Schists intersected by the Gotthard tunnel, schists from the Fichtel 

 and Eulengebirge, schists in the districts of all the geological surveys 

 have been studied and their mineral components determined. Thus 

 our knowledge of these rocks has been much extended, and one can 

 conclude that although no theories are generally adopted, a very long- 

 step has been taken in gathering together details of information, which 

 will all be systematized at some future time. 



LITHOLOGY. 



The modern methods of lithological research and the results thereby 

 achieved have never received much attention in annual records, nor in 

 any popular publications. The dropped thread can therefore scarcely 

 be with profit taken uj) as the science stood in 1879. 



Lithology has always been recognized as an important department of 

 geology, and the rocks were studied and systematized long ago. Now 

 that the methods are so much improved, and question > of composition 

 are solved with such ease, it is only a wonder to the modern students 

 how the older students found out as much as they did. By the most la- 

 borious processes at least, the talented geologists of the past generation 

 investigated with great acuteness and often discovered with accuracy 

 the partial composition of the rocks. 



The application of the microscope to lithology has now become an old 

 feature. The studies by Brewster on the gems and crystals, of Sorby 

 on crystals and on the cavities in the minerals of rocks, of Zirkel on the 

 basalts, and very many others, have long been classic. These studies 

 were made by persons of great experience and keen observational 



