50 Forbes — On alleged Hydrothermal 



In the present instance, it may fairly be questioned as to whether 

 the papers here under consideration come up to the mark, and whilst 

 Mr. James Geikie deserves the geologist's best thanks, for bringing 

 this intricate subject into the field of geological inquiry, and for 

 expressing himself with such decision and boldness as assuredly to 

 wake up the attention of such as have devoted themselves to similar 

 investigations, it must at the same time be regretted that the sub- 

 stance of the papers themselves does not prove the author to be 

 much at home either in chemistry, mineralogy, petrology, or physics, 

 and accounts for his placing such apparently implicit reliance upon 

 crude observations made in the field, and undervaluing the all- 

 important assistance to be derived from a knowledge of the collateral 

 sciences. 



In a report on the igneous rocks of South Staffordshire,^ the 

 .■writer of these remarks stated, " In these investigations it is absolutely 

 essential that the chemist, geologist, and mineralogist shall go hand 

 in hand in the inquiry," and nobody believes more thoroughly than 

 he does in the words of Mr. James Geikie, " that the question of the 

 origin of granite and other allied rocks will ultimately be solved by 

 the field observer." But he would add, however, "certainly not by 

 the mere field observer ; but by the man who, in addition to being a 

 correct field observer, brings into the field a sound knowledge of 

 chemistry and mineralogy, with the more mathematics and physics 

 the better, and who employs the microscope to assist his eye in the 

 examiuations of the more compact or apparently homogeneous rocks.'^" 



It must also be remembered that the progress of science demands 

 that the geologist, also, shall no longer put his whole reliance in a 

 pair of good legs, and plenty of field practice, but must avail 

 himself of every possible assistance and advantage afforded him by 

 the rapid strides of the collateral sciences : and depend upon it, 

 before this is done, such intricate problems as the origin of the 

 metamorphic and crystalline rocks, the formation of lodes, etc., 

 ■ stand but a poor chance of solution.' 



The writer does not speak upon the strength of an acquaintance 

 with this subject of a few months or years, but for more than 

 twenty years has continuously occupied himself in a special and 

 minute study of the crystalline and metamorphic rocks, having 

 examined them in the field over a great part of Europe, North and 



1 British Association Reports, 1865. Transactions of Sections, p. .'5 3. 



2 Geologists have not as yet learned to appreciate the true value of microscopic 

 investigation, In very many cases the simple examination of a rock section can at 

 once determine whether a rock is a true igneous rock, or the product of a secondary 

 metamorphism. The admirable researches of Mr. Sorby show how much may he 

 effected in geological research by the use of the microscope. The writer, fully appre- 

 ciating this, has devoted much time and labor since 1851 to this branch of petrology, 

 and has now above 900 sections of crystalline and metamorphic rocks from about 

 480 localities, in different parts of the world. 



3 Mohrinhis Geschichte der Erde, 1866, p. 516, gives as No. 92 of his Theses, 

 '* Geologus non aestimatur ex calceis in peregrinationibus detritis ; " it is admitted 



■that some geologists of repute are neither Palaeontologists nor Petrologists, nor much at 

 home in either mineralogy, chemistry or mathematics : it becomes, therefore, some- 

 what perplexing to define what constitutes a geologist. 



