232 Professor Connell on the 



greatest success. The family of the Ammointes had previously 

 been but little studied, and he subjected them to a minute cri- 

 tical examination, unfolding their natural distinctions, elu- 

 cidating their relations to the various formations, and de- 

 ducing the most surprising results for geognosy. He next 

 took up the Brachiopodes, a family not less difficult, and 

 not less important in the history of the earth's crust. He 

 published a separate work on the subject, which is rich in 

 valuable conclusions regarding these remarkable and varied 

 remains of a former state of things. We might still have 

 brought forward a great deal as to what our j ustly celebrated 

 countryman has contributed on particular subjects ; but the 

 space allotted does not permit me to enter into detail upon his 

 extensive and important investigations.* 



On the Chemical Constitution of Sillimanite. By Arthur Con- 

 nell, Esq., F.R.S.E., and Professor of Chemistry in the 

 University of St Andrews. Communicated by the Author. 



This mineral occurs at Saybrook, in Connecticut, and was 

 described some years ago by Mr Bowen, who found it to con- 

 tain the following constituents : 



Silica, 42.666 



Alumina^ 54.111 



Oxide of iron, 1.999 



Water, 0.510 



99.286 



From the near coincidence of these proportions with Klap- 

 roth's analysis of Disthene or Kyanite, and from the resem- 

 blance of Sillimanite to that mineral in some of its crystallo- 

 graphic and other external characters, Mr Haidinger gave his 

 opinion, that the latter mineral was probably a variety of 



Disthene. t 



More lately Dr Thomson has published an analysis of Silli- 

 manite, by Mr Thomas Muir, one of his pupils,J which gives 



* Iloffmann^s Hinterlasscne Werke. t Mineralogy, iii. 153. 



X Edinburgh Transactions xi., 245, and Outlines of Mineralogy, i. 424. 



