GEOLOGY. 233 



Evidences of the origin of many such rocks are to be obtained by the 

 study of contact i^henomena, and the true line of division between gran- 

 ite and gneiss is to be thus deduced. 



EXPERIMENTAL GEOLOGY. 



There has of late years been much less interest felt in speculative ge- 

 ology ; or rather, it has been the tendency to bring geological phenomena 

 more easily within the limits of common comprehension by showing that 

 analogous effects can be produced by very simple causes that are within 

 oar control or limits of our observation. The great work by Charles 

 Lyell on the principles of geology, in which he showed that the geo. 

 logical forces that are daily active about us, if allowed to operate a sufli- 

 cient time, would produce the results that are described by geologists 

 was a great move in this direction, and students have been ever more 

 and more active in attempting to reproduce phenomena seen in nature 

 in the laboratory. Daubree, who has been very active in this direction, 

 has brought together all his researches into a single volume, which he 

 calls " Synthetic Studies upon Experimental Geology." Here one finds 

 the results of his celebrated studies on the minerals formed by the hot 

 water in the old Eoman baths, on the minerals formed in sealed tubes 

 containing very hot water, and on the production of minerals by pro- 

 cesses of sublimation. Here, also, are detailed the results of experiments 

 designed to stratify plastic materials in imitation of rocks, to joint and 

 cleave rocks as it is done in nature, and results of experiments designed 

 to form artificially products of the nature and composition of meteorites. 

 The book is a fascinating one, and contains in addition many new facts. 



Besides this voluminous work, many contributions have been made 

 to experimental geology, some of which are referred to under the head 

 of mineralogy. It is proper to notice here the circumstance that 

 Fouque and Levy have accurately reproduced leucitic lavas like those 

 that have issued from Vesuvius, as well as nephelin-holding and other 

 common volcanic rocks. This is interesting, because leucite passes as 

 an infusible mineral, and for this reason, and because it is not always 

 the first mineral to crystallize in these rocks, the question has been dis- 

 cussed whether these lavas result from a purely igneous fusion. So far 

 as the possibilities of the case are concerned, the question may be 

 regarded as settled. 



EOZOON CANADENSE. 



Perhaps no question in American geology has excited such long and 

 bitter controversy, participated in by students who have considered it 

 from such varied standpoints, as the question of the organic or inorganic 

 nature of this form that has been found in the rocks of various lands. 

 Those who have believed in it most fully have been those most familiar 

 with its mode of occurrence, and this has always strengthened their 

 case, supported as it has been by eminent zoological authority. Yet 



