304 E. B. Bailey — 11 lb Sgurr of Evjg. 



crumbling away to earth. I feel quite confident myself that these 

 harder and softer elements correspond to the doleritic and basaltic 

 material respectively of the lava succession alongside. In agreement 

 with this 1 found in the accessible part of tlie deposit dolerite 

 fragments, one big block in particular associated with crumbling 

 amygdaloidal lumps of basalt. But Harker did not notice any dolerite 

 at all [3, p. 54], and accounted for its supposed absence on the view 

 that the deposit occupies a neck which was blown through the basalt 

 lavas before these latter had been invaded by dolerite sills. In fact, 

 the doleritic bands in the lava sequence and also the dyke marked B 

 in Fig. 3 are regarded by Harker as intrusions of later date than the 

 fragmental deposit against which they terminate so abruptly. 



The view just outlined was largely based upon an examination of 

 the accessible southern edge of the exposure, where it was thought 

 that clear evidence existed of a dolerite sill being deflected upwards 

 along the steep margin of the deposit. Dr. Harker ascribes this 

 observation to Dr. Peach. I can only say that I consider the 

 appearances relied upon entirely deceptive. Eig. 3 shows the dolerite 

 in question, a particularly strong band marked D. It caps the 

 cliff for some distance south of the fragmental deposit. If it 

 recurs to the north of the latter it must have become considerably 

 thinner in the interval so as to be no longer distinguishable from its 

 fellows. Now, suppose one walks from the south along the edge of 

 the cliff towards the fragmental deposit, one finds that the surface of 

 the dolerite as exposed rises somewhat suddenly just before the 

 deposit is reached. This has given rise to the misconception that the 

 dolerite is deflected upward as a tongue along the junction. But 

 the upper surface of the exposure is in this case merely an accident 

 of erosion : there is no change of texture, no line of vesicles, nor any 

 structure at all that I could find, to suggest that the upper surface as 

 seen corresponds closely with the original upper surface of the dolerite 

 sheet. But of more importance than this negative observation are 

 the actual appearances presented at the junction of the dolerite and 

 the fragmental deposit, appearances which seem to have been hitherto 

 quite overlooked. The pebbly material is packed into little hollows 

 in the steeply truncated face of the dolerite. The deposit has not 

 been indurated. The dolerite, even at the contact, maintains its 

 doleritic texture without the least sign of chilling. I left the 

 exposure convinced that this dolerite sheet (whether it be lava or sill 

 I am uncertain) is of earlier date than the fragmental rock, and that 

 the latter has been heaped against it. 



Now the bearing of all this upon the point at issue is that Harker 

 claims to have demonstrated that the fragmental deposit is earlier 

 than a suite of dolerite sills, in their turn earlier than the pitchstone ; 

 that, in fact, a great epoch of sill-intrusion separated the period of 

 formation of the deposit from the period of the advent of the pitch- 

 stone ; and accordingly that the conjunction of the fragmental deposit 

 and the pitchstone must be fortuitous.. If my criticism is justified, 

 this line of argument can no longer be maintained. 



We shall now briefly consider another objection of a very 

 different type. 



