INTRUSIVE IGNEOUS BODIES 303 



includes two types, i. The Batholith and 2. the Stock and Boss. 

 The distinction between these two groups is largely one of size. 

 Batholiths are large intruded masses of granitic or other holocrys- 

 talline pyrogenics, such as form the central granite core of mountain 

 masses. Suess holds that these masses are intruded through the 

 adjacent formations as a result of fusion, constituting thus a 

 transfusion mass or Durchschinchiiugsniasse. A boss (Fig. 40) is 

 a subterranean intrusive mass of moderate size with a circular or 

 subcircular ground plan. The term has been used for such masses 

 up to several miles in diameter, but is best restricted to the smaller 



/ 

 / 





' /'A^/ '/■'■-- -^-v.>(~%.^^ 



Fig. 41. Ideal section of the Holmes Bysmalith (after Iddings). 



masses of this type. A stock, on the other hand, is characterized by 

 irregularity of shape, and often by smaller size than that of the 

 boss. 



The Hypabyssal intrusives may be divided into : 



I. The transverse or those injected across the planes of stratifi- 

 cation of the invaded formation, and 

 II. The parallel or those injected along the planes of stratification 

 of the invaded formation. (Daly-7 : 507.) 



The first of these groups includes, i. Dikes, 2. Eruptive veins, 

 3. Apophyses or tongues, 4. Bysmaliths, 5. Necks, and 6. Chono- 

 liths. A dike (Fig. 44) is characterized by nearly or quite paral- 

 lel walls, relatively close together, and may cut the planes of strati- 



