ANNIVERSARY ADDRESS OF THE PRESIDENT. xlix 



semi-fusion, whatever strata they may chance to come in contact 

 with, of whatever age those strata may be." 



From the mode in which the equivalent of the Caradoc sandstone 

 reposes on the Longmynd beds, lying unconformably upon them, and 

 from being composed of water-worn pebbles derived from them, the 

 authors infer that this accumulation formed the coast boundary of 

 the sea of the time. So that from this circumstance and other facts 

 noticed. Professor Ramsay and Mr. Aveline consider the Longmynd 

 country to have constituted dry land washed by a sea at a level equal 

 to the Caradoc sandstone accumulations of the vicinity. 



Tracing the western boundary of the Caradoc sandstone northward 

 it is found several hundred feet above the Bala limestone, north-east 

 from Dinas Mowddy, and in its progress north and west it gradually 

 creeps over the various beds, so that at Yspytty Evan it occurs at 

 the level of that limestone, proving an overlap. Approaching Builth, 

 the Caradoc series turns off eastward, as if the boss of older rocks to 

 the northward of that place had formed a barrier to their further 

 extension in that direction. Further south they have not been seen, 

 and they would appear there and around the older rocks of Builth 

 to be overlapped by the Wenlock shales. 



The authors infer, from the unconformity of the Caradoc and Wen- 

 lock deposits, in connection with the old coast-line of the Longmynds 

 and Bishop's Castle series, that both at Builth and Bishop's Castle, 

 the older rocks rose above the level of the sea at the time when the 

 Caradoc sandstone was formed, this land becoming gradually de- 

 pressed during the deposit of the Wenlock and Ludlow rocks. Thus 

 this dry land became covered by thousands of feet of sands and mud 

 mingled with the remains of marine animals, geological changes having 

 now again brought this old surface, denuded of its great covering, 

 above the level of the sea, so that it again forms dry land. 



It will be scarcely necessary to call attention to the importance of 

 these facts and the views connected with them. Deposits of the age 

 of theLlandeilo flags, with the older strata on which they repose, upset 

 and bent, rising above a sea, and by their loss from breaker-action 

 on the coasts and the abrasion from atmospheric influences inland, 

 forming sand and mud beds around them, in which the remains of 

 the marine animals of the time became entombed, and this at a 

 period when, as far as our present information extends, the earliest 

 kind of life established on our globe was yet unchanged in its general 

 character. Thus it is that by careful and minute study we obtain a 

 glimpse of the probable distribution of land and sea at this period in 

 part of the area now occupied by the British islands, — much doubtless 

 that was then contemporaneous as dry land being cut away by denu- 

 ding forces during the progress of geological time, the matter removed 

 transported around, much of it often used over and over again, con- 

 stituting other rocks, and a large portion of the old rocks which may 

 be still remaining in their places of original deposit being covered 

 over by these more modern deposits, or concealed beneath the sea. 



Mr. Beete Jukes and Mr. Alfred Selwyn have presented us with a 

 sketch of the structure of the country extending from Cader Idris to 



VOL. V. PART I. d 



