306 



Adventures in Scenery 



companied or closely followed by intrusions of diorite. The 

 Mariposa rocks likewise were intruded and metamorphosed in 

 late Jurassic or early Cretaceous time. The Mariposa rocks 

 were folded, closely crowded together, and complexly infolded 

 with the Calaveras rocks. After the rocks had been folded and 



Courtesy U. S. Bureau of Mines 



FIG. 87. Barite mine and mill. National Lead Company, on Merced River 

 near El Portal (left) . At right, open-cut in barite mine, with openings into stopes. 



given their steeply dipping attitude great volumes of magma 

 invaded the crust. 



"The fissuring of the Mother Lode is regarded as due to com- 

 pressive stresses. The stresses that caused them were related to 

 the mountain building of the Sierra Nevada, lying to the east. 

 The compressive stresses were so great that the rocks in their 

 path yielded to the intense folding. The stresses, though resist- 



