978 REVIEWS 



into the surrounding sedimentary rocks. Their strike is generally 

 north and south, northeast and southwest, and northwest and south- 

 east. Only one was noticed with an east and west strike, and their 

 course is accordingly frequently nearly at right angles to the trend of 

 the mountains. They are most commonly from one-half to one meter 

 in width, the monchiquites being particularly variable. As a whole 

 they form a series of differentiated rocks genetically related to the main 

 elaeolite syenite. The observed types are : bostonite-porphyry, 

 tinguaite, nepheline-syenite-porphyry, camptonitic tinguaite, and 

 camptonitic and monchiquitic rocks. 



The petrography of all the rocks mentioned has been worked out 

 with considerable detail, and is accompanied by several chemical 

 analyses, forming a valuable contribution to the literature of these 

 interesting types. It is shown that the nepheline-syenite of the Foia 

 is poorer in the nepheline than the rock of the Picota, and closely 

 resembles the pulaskite of Arkansas. It presents many features which 

 point to a quicker solidification at less depth than is indicated in the 

 case of the Picota facies. The study of the dike rocks brings out 

 many interesting and suggestive points which can only be referred to 

 in a brief review. With the suggestions embodied in Pirsson's recent 

 paper^ on the analcite series of rocks in mind, the role played by that 

 mineral in these Portuguese rocks, and the description of a so-called 

 " leucite-tinguaite-vitrophyre" with its high alkali contents and 

 devitrified glassy base, become doubly interesting. 



The microscopic petrography of the altered sediments is minutely 

 described, and the paper ends with an excellent summary, in which the 

 general sequence of the intrusive activities is presented. The plutonic 

 mass of the Picota, slowly cooled at great depth, is the oldest portion 

 of the massif, and probably also underlies the rock of the Foia, which 

 is regarded as an already somewhat differentiated, more acid, upper 

 portion, which solidified nearer the original periphery of the mass. 

 Certain schliere in the Picota area are similar to the rock of the Foia. 

 Corresponding to these more acid differentiation products, are 

 the tinguaite dikes, as later intrusions or Nachschiibe. Basic differ- 

 entiation products are represented by slowly cooled theralitic rocks 

 (essexite and teschenite), and their corresponding dikes of the 

 camptonite-monchiquite series. These rocks are thought to be 

 younger than the tinguaites, but no satisfactory evidence was obtained 



' This Journal, Vol. IV, p. 679. 



