INTRUSIVE IGNEOUS BODIES 



307 



Phacoliths (Harker-15 i/d) are intrusions of igneous rocks 

 between strata which have been folded and occupying the points of 



N.W 



Fig. 48. Lenticular intrusion (phacolith) in anticline of Ordovicic strata, 

 Corndon, Shropshire, England. (After Lapworth and Watts.) 

 A. Flags and shales; B. ashes and andesite; D. dolerite. 



greatest pressure relief, as in the crests and troughs of a simply 

 folded series of strata. (Figs. 48, 49.) As Marker points out, they 



Fig. 49. Diagram to illus- 

 trate phacolith intrud- 

 ed in connection with 

 folding. (After 

 Harker.) 



Fig. 50a. Hypothetical development of a 

 folded laccolith. ist stage. 

 (After Baltzer.) 



differ from laccoliths, in that they are a consequence of folding, 

 instead of the cause of the uplift as in laccoliths. Their distinction 

 from the Chonoliths of Daly lies in their parallelism to the strata 



Fig. 50b. The same as Fig. 50a, in the 

 second stage (Baltzer). 



Fig. 50c. The same, in the third stage 

 (Baltzer). 



between which they are intruded, while chonoliths are irregular, 

 commonly, in part at least, transverse. A typical example of a 

 phacolith is seen in the accompanying section from Corndon, Shrop- 



