203 



is now very strongly polarizing, and in the transformation 

 seems to have gone over into a carbonaceous mass. Obviously 

 these rocks when fresh had an unusual chemical constitution, 

 showing their affinity with the more divergent types, to which 

 I will now pass on. 



c. Basic rocks of lamprophyric type. The group of rocks 

 to which 1 have now come is closely connected by means of 

 intermediate links with the last-named group. Yet its consti- 

 tution is throughout more basic: most of the rocks contain 

 normally neither orthoclase nor quartz, and in some varieties 

 no Porphyrie felspar occurs at all. As the samples were 

 mostly collected as blocks it is possible that some of the 

 varieties do not appear as independent forms but as subordinate 

 transition forms or small differentiated sections in the main 

 mass. However, it is impossible to give a certain proof of 

 this; I shall therefore describe the most interesting forms without 

 expressing an opinion about their reciprocal connection. 



One of these rocks shows macroscopically large — up to 

 a centimetre in length — isolated crystals of felspar (orthoclase) 

 and of green chloritic mass, as well as numerous irregular 

 miarolitic cavities filled with calcite, surrounded by a ring 

 of small red quartz individuals; elsewhere, too, quartz occurs 

 as the last product of crystallization. Under the microscope 

 can be seen, moreover, of large individuals only chlorite, whose 

 origin I could not determine; the rock also contains a good 

 deal of apatite. The ground-mass itself consists to a great 

 extent of irregular lath-shaped felspar and of minute scales of 

 chlorite which in thin sections vividly recall the aegirine needles 

 in certain tinguaites. It is possible that this rock should be 

 referred to bostonite. 



Here belongs another variety with solitary felspar crystals, 

 completely transformed, with numerous areas in which calcite 

 and often idiomorphic individuals of quartz occur together in a 

 way that suggests an origin associated with the last period of 



