1853.] RAMSAY— LOWER PALAEOZOICS OF N. WALES. 171 



The faintest traces of its ashes are associated with and underlie the 

 Bala limestone in the Bala country. The great centre of the older 

 volcano or volcanos was further to the south-east. 



Now it is worthy of remark, that the great bosses and lines of in- 

 truded felspar- and quartz-porphyries, greenstones, and syenites are 

 always found in rocks as old as or older than the rocks with which the 

 ashes and lava-flows are associated. My belief, therefore, is that they 

 form the original deep-seated nuclei that were connected underground 

 with the volcanic rocks that in this neighbourhood are interstratified 

 with the Lingula and Bala beds. Further, that the long lines of 

 greenstone that are associated with the rocks lying between Snowdon 

 and Moel-wyn bear the same relation to the Snowdon volcanic series 

 that similar greenstones do at a lower level to the volcanic series ol 

 the Arenigs and Arans ; and that, instead of being contemporaneous, 

 as implied by Professor Sedgwick, they merely originated in melted 

 matter, being injected and burrowing into lines of weakness deep un- 

 derground during two periods of volcanic activity, and that both they 

 and the greater masses of intrusive porphyry and syenite have all 

 been subjected to those subsequent forces that bent and contorted 

 the whole of the ancient palaeozoic rocks. From an examination of 

 many sections, I have no doubt that the greater intrusive nuclei par- 

 tially partake of these contortions, because in the upward progress of 

 the melted matter towards the volcanic mouths it sometimes was more 

 or less injected in great sheets somewhat in the lines of bedding, 

 while sometimes it broke across the beds with comparative abruptness. 

 When in sheets, there is no reason why it should not have been 

 equally bent with the thick masses of truly interstratified porphyries. 

 They are certainly affected by faults in the same manner as the strata, 

 and if so, they can in no sense be looked upon as the cause of the 

 great disturbances that contorted and faulted the country. These 

 were of later date. 



I have said that the intrusive traps are oi the same general dates 

 with the interstratified igneous rocks. The mass that runs from St. 

 Ann's Chapel to Llanllyfni is a quartz-porphyry. Crystals of quartz 

 are imbedded in a felspathic base. The neighbouring mass, nearer 

 the Menai, often much resembles it, but is also much more granitic 

 in texture. The Anglesea granite often quite resembles the Menai 

 igneous rock, and sometimes by addition of mica becomes a true 

 granite. There is no reason why they should be referred to different 

 dates, and, if the previous conclusions be correct, then the granite is 

 of Lower Silurian date, and the metamorphism of at least part of the 

 Anglesea rocks took place at one of the previously mentioned periods 

 of volcanic activity, and probably at a depth of not more than from 

 8000 to 10,000 feet beneath the surface*. As the granitic rocks of 

 Anglesea and the Menai break out at many places and at many dif- 

 ferent levels, there is reason to conclude that the island generally is 

 underlaid by a great mass of granite ; and, if this be so, then it may 

 be probable that all the altered rocks of Anglesea were principally 



* The Lingula flags and superincumbent Bala beds thin out considerably be- 

 tween Bala and the Menai. 



VOL. IX. PART I. N 



