362 TRANSACTIONS OF THE 



the outcroi^s and of the valley is northwest and southeast; hut there are 

 several local variations. 



These slates are generally light colored or drah at the surface; but in 

 depth they are black, like roolii]g slate, and break up into rhomboids. 

 This is particularly well shown at the Princeton Vein. There are nume- 

 rous intercalations of sandy layers passing into sandstones — sometimes 

 into coarse grits, and even pebbly beds, and beds of slaty conglomerate. 

 The softer and most finely laminated portion of the group is generally 

 found near the medial line of the valley, and is the point at which the 

 Princeton Vein occurs. It is near this part of the series, at the north- 

 ern end of the estate, that the Jurassic fossils occur. 



The following is an approximate geological section of the estate, at 

 right angles to the course of the rocks, and nearly over the Princeton 

 Vein. It is a composite section, being made up of three distinct portions 

 where the observations had extended, but all near together, so as to pre- 

 sent a ftiir view of the sequence of the formations. The wdiole embraces 

 a distince of about four miles, according to the scale of the small pub- 

 lished map of the estate. The southwestern end is taken along Bear 

 Creek, the middle portion across the Princeton Vein, and the remainder 

 on a line near Upper Agua Fria, northeastei-ly to Bullion Eidge. The 

 following is the sequence of formations from west to east : 



SECTION ACROSS THE MARIPOSAS. 



1. Coarse, heavy conglomerates, metamorpliosed — Bear Mountains. 



2. Compact crystalliue slates ; crystalline cleavage. 



3. Conglomerate ; slaty. 



4. Argillaceous slates, regularly stratified ; thick series. 



5. Siindstone and sandy beds, (thin.) 



6. Princeton gold vein ; quartz three fgct thick. • 



7. Argillaceous slates and quartz veins; the horizon of the Jurassic fossils. 



8. Magnesian rock and quartz veins. 



9. Pine Tree or "Mother Vein," or its extension. 



10. Argillaceous slates. 



11. Conglomerate; slaty. 



12. Compact slates. 



13. Greenstone, limited in extent; probably a metamorphosed sandstone. 



14. Sandstones and saudj' slates. 



15. Serpentine and magucsian rocks — the northern extension of Buckeye Ridge. 



16. Compact slates, crystalline and much metamorphosed. 



17. Conglomerates and sandstones, heavy and massive; the so-called "greenstone" of Mount 



Bullion Range. 



This is the general outline of the formations. Both of the bounding 

 ranges of the valley are formed by the heavy metamorphic conglome- 

 rates, so miich altered and changed as to be scarcely recognizable. They 

 are generally supposed to be formed of greenstone, and in some j^laces 

 they do not give any evidence of their sedimentary origin; in others, 

 the outlines of the pebbles and boulders are distinct. These boulders 

 are remarkably large and heayj''. From the general similarity of the 

 rocks of these two ranges — Bear Mountain on the west and Bullion Eange 

 on the east — together with the succession and character of tlie forma- 

 tions between, I am led to regard the whole series as a fold or plication, 

 and the valley as either synclinal or anticlinal — probably the former."^ 



■*The above section of the gold formation of the estate, and the substance of the observations 

 upon it, were given in a report to F. L. Olmsted, Esij., in eighteen hundred and sixty-four. Incditcd. 



