Parr VIL. Szcr. i. § 4] VOLCANIC NECKS. 559 
shaped hills (Fig. 287). . This contour, however, is not that of the 
original volcanoes, but is due to denudation. Occasionally the rocks 
of a neck have been so worn away that a great hollow, suggestive of 
the original crater, occupies their 
site. (Fintry Hills, Stirlingshire.) 
The dotted lines are sug- 

Fig, 286.—PuLan oF NEcK, SHORE, NEAR 
St. Monans, Fire. 
11, bedsof limestone; c,thincoal-seam; B,basalt ~~. AXdeSY//-//// 
veins; S, large bed or block of sandstone. LSA > yy Lf 
The Neck measures about 60 by 37 yards. BSA Ch { 
The arrows mark the dip of the strata. SF DAI LANCET iW ea 
Tt might be supposed that necks : ee Yi 
should always rise on lines of fissure. NERS 
But in central Scotland, where they 
abound in rocks of Carboniferous 
age, it is quite exceptional to find 
one placed on a fault. As a rule, 
they seem to be independent of the 
structure of the crust through which 
they rise. | 
The materials filling up ancient 
volcanic orifices may be (a) some 
form of lava, as felstone, quartz- 
porphyry, diabase,- porphyrite, 
basalt; or (6) the fragmentary 
materials which fell back into the throat of the volcano and finally 
solidified there. In many instances both kinds of rock occur in the 
same neck, the main mass consisting of agglomerate or tuff with a 
central pipe or numerous veins of lava. Among the Paleozoic 
Fic. 287.—SnctTion oF THE Vou~cANIo Nox or Larco Law, Fire. 
1 1, Lower Carboniferous strata; ¢, tuff of cones; ¢’, tuff of area around the cones; B B, basalt filling central pipes 
of the vents and lateral veins; B’ basalt, which may have flowed out at the surface. 
-gestive of the original outline of the hill. . 

