QUARRIES—DISLOCATIONS OF THE STRATA. 
149 
the stone from a bank or elevation; in addition to the inconvenience of working a quarry in this 
form, the waters of the bay percolate through the bank and accumulate in the lower part of the 
excavation. The bank of stone does not, however, rise much over 30 or 40 leet above high- 
water mark, and it is very much decomposed and broken up, so that the excavations are neces¬ 
sarily below tide. 
Large blocks of stone are taken out of this place. They split readily into various desired 
sizes, and are easily cut and chipped. When dressed or hammered, the surface has a pleasing 
shade of color, which is much lighter than the bluish-green stone of Yerba Buena, being more 
gray. Fragments of the stone effervesce briskly when placed in dilute hydrochloric acid, and 
many of the blocks are traversed by thin veins and seams of white, crystalline carbonate of lime. 
Where these veins are exposed on a weathered surface, they stand out above the sandstone, 
showing their superior resistance to degradation. 
The slaty character of some of the beds is well seen in the excavation. Thin layers of only 
a few inches in thickness occur between the beds of solid stone. These slates or shales are darker 
than the sandstone, and appear to have been subjected to great pressure. Many bendings and 
plications of the strata have occurred at this locality, and at one side of the quarry there is an 
interesting dislocation and fault of one of the beds, which bears interesting testimony to the 
action of violent compressing forces. This dislocation is represented in the figure. 
DISLOCATION OF A BED OF SANDSTONE, STATE’S PRISON QUARRY. 
This bed must once have been continuous, the several parts being joined on to each other in 
the order in which they are numbered. It is now broken in three places, and the two ends of 
the main portions were pressed together so as to throw out a fragment on each side. The space 
between the blocks is occupied by highly contorted and crushed shales, enclosing some angular 
fragments of sandstone. 
Stone from this quarry, roughly broken out into blocks, was selling in the city of San Fran¬ 
cisco for ten dollars a ton—[1854.] It is readily chipped and dressed, and, when hammered, 
makes a good surface for the fronts of buildings. It is certainly a valuable building material, 
and is far superior to the partly decayed and friable stone from the Benicia beds. 
Another interesting outcrop of the strata is found at Marin island, a small island about four 
