INTRODUCTION. 



A complete geological collection of the rocks of any 

 country should comprise three suites : 



1st. Lithological, illustrative of the nature of 



rocks. 



2nd. Stratigraphieal, illustrative of their order of 



succession. 



3rd. Topographical, illustrative of their geogra- 

 phical distribution. 



The space available in the Museum for the display 

 of rocks is barely sufficient for one 

 and the first has been chosen as af 



one of these classes, 

 is affording a simple 

 method of instructing all who wish to learn what are 

 the external characters of such rocks as conglomerate, 

 sandstone, grit, limestone, shale, schist, gneiss, granite, 

 the different kinds of trap, lavas, volcanic ashes, and 

 indeed all the varieties of stony substances that are of 

 common occurrence. To descriptions of the rocks in 

 the Cases, an index has been added, indicating the 

 stratigraphical relations of the specimens, or in other 

 words, the order of succession in which the rocks 

 were formed from whence the specimens were derived. 

 {See p. 279.) 



a 4 



