174 Adventures in Scenery 



Roof Rocks Reveal History of Ancient 

 JAountain Systems 



"The age of the metamorphic rocks of the Sierra Nevada 

 is not easily determined owing to the scarcity of fossil remains 

 preserved in them. A few fossils, however, have been found, 

 particularly in the limestone and sandstone of the lower belt. 

 From a study of these fossil remains it has been determined that 

 the rock strata of that belt fall into two distinct series, one of 

 which is much older than the other. The older, known as the 

 Calaveras formation, is of Palaeozoic (Carboniferous) age; the 

 younger, known as the Mariposa formation, is of Mesozoic 

 (Jurassic) age. The older rocks make up approximately the 

 eastern half of the belt; the younger rocks the western half, 

 extending down to the foothills. 



"In the strongly deformed structure of these two distinct 

 series of strata there is clear evidence of the former existence 

 of two successive mountain systems. The general character of 

 these ancient mountain systems is indicated by the forms, mode 

 of arrangement, and trends of the folds. The tops of the up- 

 folds doubtless were worn away at an early stage during the 

 slow progressive upheaval. Stumps of resistant upturned 

 strata remain."* 



Thus it is seen that the Sierra Nevada Range is an uplifted 

 block, pushed up to a great height by the up-welling from the 

 depths of the earth of molten rock. The molten rocks of the 

 intruding batholith slowly cooled and crystallized beneath an 

 overlying roof of sedimentary rocks. In the lapse of time since 

 the intrusion of the molten rock the rocks that were uplifted 

 and formed the roof of the great uplifted dome have been 

 eroded away, and the molten rocks, cooled and crystallized, 

 are exposed and form the greater part of the surface of the 

 present range. 



* Francois E. Matthes. Op. cit. 



