516 DR. C. CALLAWAY ON THE LONGMYNDIAN [Allg. I9OO, 



not uncommon. The surfaces formed by jointing and crushing are 

 ordinarily stained by a blackish substance, which is opaque in 

 transmitted light, and is possibly iron-oxide. On some of the 

 surfaces is seen a thin coating of a pale-green mineral, which I 

 cannot positively identify. Some of the mica also seems to have 

 been formed in cracks as the result of infiltration (see p. 513). 

 But such cases as these do not prove the action of high temperatures. 

 On the other hand, the fragments in the grit retain their angularity, 

 and the rock as a whole is as unchanged as an ordinary grit 

 from the Longmynd. The infiltration that has taken place is the 

 natural result of a very moderate degree of crushing, which has 

 permitted the access of water. The mineral deposits in the cracks 

 may easily have been derived from the rock itself. 



(b) The Woolhope Limestone. 



I have already referred to the sections at Yat Hill, and remarked 

 that, except at one point, the rock exhibits no clear bedding. A 

 little farther south, near Dolyhir llailway- station, the limestone is 

 well exposed in a large quarry, and here also I could detect no 

 stratification. The rock is massive, traversed by joint-planes 

 hading at high angles, in places crushed into a breccia, and in part 

 crystalline. The fossils that I collected were Favosites, of both the 

 (jothlandiea and Jlbrosa-types, a brachiopod (probably JStrophodonta), 

 traces of small trilobites, and fragments of crinoids. I followed 

 the limestone for | mile or so to the west, and saw several sections, 

 both natural and artificial ; but in the course of a somewhat rapid 

 examination I could find no clear stratification. The bedding there- 

 fore has been for the most part obliterated, but the presence of 

 fossils shows that the metamorphism is not intense. 



According to Murchison, 1 the alteration undergone by the lime- 

 stone is due to 



4 the action of heat issuing along a line of fissure, which, emitting the igneous 

 rocks of Stanner, Worsel, and Hanter, fused the strata into huge amorphous 

 masses, and left films of serpentine on the faces and joints of the altered 

 limestone.' 



I did not find any of this serpentine ; but, if it were present, it would 

 give no support to Murchison's contention. 



I may at once remark that the change which the limestone has 

 undergone is not such as we are accustomed to expect at the con- 

 tact with an intrusive igneous mass. So far as I could ascertain, 

 the rock contains no foreign minerals whatever. What we do find 

 is a certain amount of crushing, and a partial recrystallization. 

 The microscopic examination of three slides reveals the nature of 

 the change produced : — 



[559] Prom the quarry south of Dolyhir Eailw ay-station. 



This specimen was selected as containing small rounded patches of a finer 

 grain than the bulk of the rock. These, when enlarged, are seen to be organic 

 bodies of the nature of either Stromatopora or Favosites, consisting of an 



1 ' Siluria' 4th ed. (1867) pp. 108-109. 



