270 Adventures in Scenery 



The beautiful blue calcite crystals occurring in the Sky Blue 

 Hill were formed out of mineralized solutions. The two hills, 

 Sky Blue and Chino, differ greatly in the effects of meta- 

 morphism. The limestone of Chino Hill was converted into a 

 white marble and is little mixed with other minerals. It was 

 not invaded by the later invasion of igneous rock, as was that 

 of Sky Blue Hill, where the blue calcite is mixed with various 

 metamorphic minerals. 



The occurrence of the great number of minerals in the 

 highly metamorphosed limestone of these hills is a subject of 

 interest (more than 50 minerals have been described from this 

 locality) . Our purpose is study of the geology of the forma- 

 tions and not the minerals as such. The metamorphism of the 

 limestone rock was a geological event. It occurred long ago 

 from the great heat and pressure of the intruded molten rock. 

 The minerals were formed in the process of metamorphism by 

 combination of the chemical elements that were in the geologic 

 formations. 



The limestone rock in the hills is an old formation. It was 

 formed on a sea bottom long long ago. When the hot liquid 

 magma was intruded into it and the minerals crystallized, that 

 also was long ago (Jurassic time) . But the "hills" were not 

 there then. The land had not at that time been eroded as now. 

 The limestone extended in great beds far over the region. The 

 limestone was part of a great formation that extended over 

 many miles. Erosion during long ages carried away the lime- 

 stone. Streams flowed between hills, and the hills that we now 

 see are a little of the land that was not carried away. The 

 limestone rock is old, but the hills are young. They were 

 formed recently geologically yesterday and today. 



The mind can hardly grasp the great length of time. The 

 broad plain, of which these hills formed a part, was eroded into 

 hills and valleys. The hills were slowly worn down and carried 

 away. The hills that we see today are what is left. They are 

 remnants of the ancient plain. They were being worn away 



