MINERALOGY. 301 



liue planes, indicates that we have perhaps much yet to learn concern- 

 ing isomorphism. 



One of the most interesting studies of this period has been made upon 

 the lithium aluminum silicate spodumene and the products of its alter- 

 ations. Mr. Alexis A. Jidien, of Columbia College, first examined the 

 siiecimens that he obtained in Massachusetts. Spodumene, by the action 

 of decomposing reagents in nature, exchanges its lithia for potash or 

 soda, and becomes altered into a variety of substances, one of the most 

 characteristic of which has been called cymatolite. Mr. Julien analyzed 

 this substance and endeavored to fix its comi^osition. But at Branch- 

 ville. Profs. Brush and Dana found immense crystals which were origi- 

 nally all of si^odumene, and which had decomposed in such a way as to 

 enable them to make a most interesting investigation and arrive at new 

 results. These crystals were of very great dimensions, some being over 

 four feet long and a foot wide. Their interiors were still of a beautiful 

 clear pink si)odumene, but they were mostly altered into mica, albite, 

 cymatolite, and a translucent substance which they provisionally called 

 /3 spodumene. By chemical and microscopic study they demonstrated 

 that this so-called cymatolite was comi)osed of a very intimate mixture 

 of white mica and albite, and that tlic [i spodumene was composed of 

 albite and a new mineral, which they have called eucryptite, and which 

 will be found described beyond. The study of such processes of altera- 

 tion is very important, since it develops facts of geological importance, 

 and the changes which this spodumene has undergone form an inter- 

 esting chapter in the history of jiseudomorphs. 



Mr. Harrington, of Montreal, has made an important study of the apa- 

 tites and their associated minerals in Canada. As is well known, very 

 large deposits of clear green and otherwise colored apatite occur there 

 from which ver}^ large quantities are annually taken to be crushed and 

 manufactured into superphosphates for agricultural purposes. Such 

 deposits also occur in Norway, where they have been studied by Pro- 

 fessors Brogger and Reusch, who determined them to be of eruptive 

 origin. Professor Harrington, after showing that they occur in rocks of 

 a similar nature, though unlike in detail, shows that there is abundant 

 reason for considering that they are not eruptive rocks, and thinks that 

 they were gathered by and crystallized from solutions. I will recall in 

 this connection that 31. Daubree made apatite in a closed tube, by 

 causing a volatile phosphorous compound to act upon hot limestone, 

 and he thinks that some such deposits may have been formed by subli- 

 mation. The opinion of Dr. Harrington is sustained by the previously- 

 formed opinion of Dr. Hunt, and it will be seen that every possible mode 

 of origin has to-day weighty ojiinion in its favor. But argument of 

 such (piestions is progress, and is a long step toward conclusion, and 

 these studies have contributed much to our knowledge of these deposits. 

 IMr. Harrington describes immense crystals of apatite a foot or more in 

 diameter and several feet long. Mr. Adams and Mr. Hofmanu have 



