Washington — Catalan Volcanoes and their Rocks. 229 



scriptions which follow it would appear that the feldspar-basalts 

 proper differ from the others both chemically and texturally 

 to such an extent that they may be considered as belonging to 

 a distinct rock group. On the other hand, it is clear, from 

 the microscopical as well as the chemical study, that the only 

 essential difference between the nephelite-basanites and the 

 limburgites lies in the presence of feldspar and in the crystal- 

 linity, the chemical composition being about the same and 

 modal and textural transition forms being common, so that they 

 may strictly be considered to be merely textural variants of the 

 same rock. But for purposes of description a distinction may 

 be made between the feldspathic and feldspar-free forms. 



In terms of the quantitative classification these basalts are 

 somewhat difficult to classify accurately without chemical anal- 

 yses. Those that have been analyzed by me, seven in number, 

 all fall in the salfemane class, and there can be no doubt that 

 all the others may be safely referred to the same chief division. 

 As regards the order, the great majority of those analyzed fall 

 in the sixth, the lendofelic portugare, only one of the analyzed 

 rocks falling in the perfelic order gallare. But this ordinal posi- 

 tion is correlated with easily distinguishable microscopical dif- 

 ferences, so there is little or no hesitation in referring the unan- 

 alyzed specimens to the one or the other order. For the most 

 part these rocks are alkalicalcic, the greater part of those anal- 

 yzed falling in limburgase, with the perfelic one in camptonase, 

 and a few in the domalkalic monchiquase : but these differences 

 in rang are not discernible by purely microscopic means. As 

 regards the subrang they are all dosodic without exception, the 

 subrangs represented being camptonose, monchiquose, and lim- 

 bnrgose, so that we are safe in assuming that the unanalyzed 

 rocks are likewise dosodic, however uncertain we may be in 

 regard to their proper rang. 



For purposes of description* the camptonose rocks, which are 

 all referable to one type and which are readily distinguished 

 from those belonging to the other divisions, will be considered 

 first. In view of the impossibility of discriminating micro- 

 scopically between the limburgose and monchiquose rocks, 

 these will be described together, but considered under the 

 head of two distinct types, a feldspathic and a non-feldspathic, 

 which correspond with the current groups of nephelite-basanites 

 and limburgites. 



The several types will not be named here in the systematic 

 and definitive manner proposed for the quantitative classifica- 

 tion, that is, by the use of a root derived from the name of a 



* In the following descriptions many terms will be used which have been 

 recently proposed. Cf. Cross, Iddings, Pirsson, and Washington, Jour. 

 Geol., vol. xiv, p. 692, 1906. 



