116 



DR. CH. CALLAWAY ON THE UNCONFORMITIES BETWEEN 



Blake's communication was read, I went several times over the 

 ground and examined the critical sections foot by foot. Weathering 

 and cart-wheels had exposed new outcrops, and the evidence I 

 obtained strongly confirmed my published conclusions. The annexed 

 section (fig. 3) illustrates the main points. I will take the section 

 from N. to S. 



Eig. 3. — Section across OharJton Hill. 



c. Conglomerate. 

 g. Grit. 

 p. Pebbly grit. 

 pg. Grit and pebbly grit. 



I. Andesitic lava. 



h. Halleflinta. 



q. Cambrian quartzite. 



The volcanic grits forming the northern part of the hill do not 

 show any clear dip. The first rock that attracts attention, as 

 we keep along the western side, is an andesitic lava, showing a 

 flow-structure, which under the microscope becomes very distinct. 

 Tlie strike is about E. and W., and the dip nearly vertical. We 

 next come to the well-known conglomerate on the top of the hill. 

 It displays no clear dip or strike, but the majority of the pebbles 

 have their longer axes trending N.AY. by W. A few yards south of 

 the strike of this conglomerate, in the surface of the road, a very 

 instructive section has been exposed. Grit-bands alternate with 

 finer compact material. One of the grits is of the ordinary 

 Wrekin type, the fragments being chiefly felsite. Separated 

 from this by a compact seam is a coarser grit of which the 

 fragments are mainly quartz, red felspar, and red granite, some of 

 the larger pieces being well rounded. Small pebbles of mica-schist 

 also occur in this band. Thus, within 2 feet in the same solid mass, 

 we have one bed which is distinctly Uriconian, and another of the 

 type which Prof. Blake would probably call " Cambrian." The 

 strike of these beds is clearly N.AV. by W., and therefore parallel 

 to the conglomerate. 



We next come to the well-known section seen in the northern 

 bank of the hollow road to the S.E. of the last spot. Prof. Blake's 

 drawing * shows a mass of structureless halleflinta with the 

 surface hollowed into two depressions in which lie small sj'uclines 

 of " Cambrian grit." He says that the grit, in two masses, dips 

 •' in certain parts towards the W., but becomes almost horizontal 

 through disturbance." At only one spot could I find a westerly 

 dip ; but the rock was dolerite, and the sloping slabs are produced 

 by joint-planes. Nor could I detect horizontal bedding ; but, since 

 the strike of the beds is nearly parallel to the section, the outcrops, 

 viewed from a distance, appear nearly horizontal. Caution is there- 

 fore necessary in working out the stratification. As we descend the 



* Quart. Journ. Geol. See. vol. xlvi. (1890) p. 409. 



