Fairbanks. | 



Ana/cite Diabase. 



299 



EXPLANATION OF PLATES. 



The letters in the figures refer to the following minerals: F, feldspar; P, 

 pyroxene; O, olivine; A, analcite; SF, secondary feldspar; M, magnetite; Pr, 

 prehnite; C, calcite; G, green matty areas. 



PLATE 15. 



Main body of the Cuyamas dike. This section shows the larger 

 undecomposed areas of analcite and the diabase granular struc- 

 ture, x 25. 



Large secondary dike (Cuyamas eruptive). The angular form of 

 the analcite replacing the feldspar is characteristically illustrated ; 

 also the fibrous alteration which the analcite in the wedge-shaped 

 areas is undergoing, x 35. 



Large secondary dike (Cuyamas eruptive). The main feature in 

 this illustration is a basal section of the lamellar pyroxene exhib- 

 iting a fibrous center due to alteration, and the peculiar ortho- 

 pinacoidal parting, x 35. 



Diallagic cleavage plate showing transverse fibration. The whole 

 width of the crystal is not shown. The fibers are seen to ter- 

 minate as a general thing on the traces of the prismatic cleav- 

 age, x 25. 



Small secondary dike (Cuyamas eruptive). One rudely hexagonal 

 form of analcite appears in contact with a wedge-shaped area 

 of the same mineral. x 35. 



Large secondary dike (Cuyamas eruptive). The prehnite is seen 

 to have its form partly conditioned by the shape of the analcite 

 area in which it occurs, x 35. 



PLATE 16. 



Figure 1.— Section from large secondary dike (Cuyamas eruptive). This section 

 shows the prehnite crystals occupying a portion of an angular 

 analcite area. The individuals do not seem to have grown from 

 the feldspar inward, but to have been formed within the anal- 

 cite. x 35. 



Figure 2. — Large secondary dike (Cuyamas eruptive). The characteristic 

 features of this section are the sharply defined areas of analcite 

 in the feldspar, the idiomorphic prehnite, the fibrous alteration 

 product of the analcite, and the rod-like form of the magnetite. 



x 35- 



Figure r.— 



Figure 2. — 



Figure 3. 



Figure 4. 



Figure 5.- 



Figure 6. 



