INTRODUCTION 197 



1. 



INTRODUCTION 



Classification and Arrangement 



The classification of building stone may be geological, 

 according to the formations whence it is obtained, and fol- 

 lowing the systems of rock classification, in which the min- 

 eralogical and chemical characters serve as the basis for 

 division into species and varieties, or it may be architectural. 

 In which the use determines the arrangement of all the 

 common kinds of stone In a few large groups. A strictly 

 geological classification according to the horizon or age of 

 the formation is however somewhat arbitrary and artificial, 

 as stones almost Identical in composition may be found in 

 formations which are of different ages. Sandstones and 

 limestones, for example, occur in all ages. What may be 

 called the architectural arrangement, as granites, marbles, 

 freestones, flagging stones, etc., is open to the objection of 

 being indefinite, confusing and unscientific. 



The division into groups or classes and species or kinds, 

 based upon differences In their mineralogical constitution, 

 is scientific and practical within certain limits. The subdi- 

 visions may not all be readily Identified by the practical 

 worker, or evident to the unaided and untrained eye, but 

 the larger classes of stone are recognized by all and at 

 once. The acquaintance with the varieties In them Is a 

 matter of education. Although the arrangement according 

 to geological horizon does not serve to mark the larger 

 divisions, it is convenient in description, and particularly In 

 so far as it is also geographical and Indicative of the groups 



