78 PEOr. A. E. G-EEEX OX A SECTION XEAE LLA^-B£EIS. 



quite as marked as those of the present section, -vrMch are purely 

 local and -svould be found to disappear if "vre were able to trace the 

 junction of the two groups of rocks over a lai'ge area. 



The remaiader of the section along the railway explains itself; 

 but I may mention that the natui'e of the junction between the 

 conglomerate and quartz-felsite at the north-western end is doubt- 

 ful ; it may be a fault, but there is nothing whatever to show 

 whether it is or not. The matrix of the conglomerate is very 

 instructive ; it is mashed up and reaggregated felsite, and it has 

 been so little altered by the breaking-up, and has been so firmly 

 bound together again, that it bears a very close, though of course 

 superficial, resemblance to the felsite itself. This resemblance does 

 not altogether disappear even under the microscope. The pressure 

 which the conglomerate has undergone has squeezed the fine portion 

 of the matrix into wavy flowing bands which bend round the blebs 

 of quartz, so that a structure has been set up in this clastic rock 

 which simulates most closely the fluxion- structure of the felsite 

 itself. The quartz crystals and blebs, too, of the conglomerate have 

 often been so little damaged during the disintegration of the felsite 

 that they still retain exactly the same appearance as in this latter 

 rock. Lideed if we cut a slice from the conglomerate so as to steer 

 clear of pebbles, it would very frequently be undistinguishable under 

 low powers from a slice cut from the felsite ; it is not till they are 

 magnified some 300 diameters that the difference between the two 

 comes out. 



Discirssiox. 



Prof. T. ]\I-'K. Hr&Hzs gave an explanation of the section, and 

 indicated some details showing what he regarded as the behaviour 

 of the beds. If older beds come up at the point indicated, they 

 would probably be Pebidian. He stated that the section was very 

 complicated, and the particular portion described by the author does 

 not, perhaps, carry with it the same conviction that other sections 

 do. The conglomerates are made up of the underlying rock to such 

 an extent that it is sometimes difficult to distinguish the one from 

 the other, where both are squeezed, faulted, and contorted. The 

 X.E. and S.W. section, as shown, did not explain itself except with 

 the intervention of faults. The priucipal section appeared to be 

 correct in the maui ; but perhaps some modification might be neces- 

 sary in details. 



Dr. Hicks said that he had very little to add to Prof. Hughes's 

 remarks. He also would not have selected this section as the best 

 example of the unconformity between the Cambrian and Pie- 

 Cambrian in this area. The section, however, was an important 

 one, as it showed that the Pre-Cambrian rocks extend further 

 towards Snowdon than had previously been ascertained. At the 

 y.TT. end of the section there were clear indications of unconformity, 

 but masked partially by faults. From the present evidence it is 

 clear that an unconformity does exist. The important point to be 



