THE 



GEOLOGICAL MAGAZINE. 



No. XXXVI.— JUNE, 1867. 



OE,IC3-Ilsr.A.ni, -A.K-TIOXjDEJS. 



I. — On the Distribution beyond the Tertiaey Districts of 

 White Clays and Sands subjacent to the Boulder-olay 



Drifts. 



By George Maw, F.G.S., etc. 



(Pakt I.) 



THE object of the following paper is to record some further ob- 

 servations on the distribution in North Wales of deposits of 

 White Clays and Sands older than the Boulder-clay and its accom- 

 panying gravel drifts, similar to those in the neighbourhood of Llan- 

 dudno, described in the Geological Magazine of May, 1865, and also 

 to give a condensed summary of what records I have been able to 

 collect of the occurrence of similar deposits in other parts of the 

 kingdom. 



The well-defined and compact geographical disposition of the re- 

 cognized Tertiary deposits of G-reat Britain renders the occurrence 

 of beds of similar physical character inferior to the Boulder-clay, in 

 outlying districts, a matter of no little interest, and with a view to a 

 more exact comparison of these deposits in different parts of the 

 kingdom with each other and with their possible analogues in the 

 Tertiary districts, I have endeavoured to bring together in a con- 

 densed form all that has been hitherto observed of these singular 

 formations. 



North Wales. — Since publishing in the Geological Magazine of 

 May, 1865, a description of the Clay- and Sand-Pockets near Llan- 

 dudno, I have learned from Mr. Binney that he made some obser- 

 vations on them several years ago, and published a -short account in 

 the Transactions of the Manchester Geological Society, but I have 

 not yet seen his Memoir. 



The only other locality in Carnarvonshire where I have observed 

 similar deposits, is at a place called Wemdow at the back of Conway 

 Mountain, about a mile and a half from Conway, where white clay 

 and sand are visible in several of the ditches. Some pits were 

 opened a few months ago with the object of working the clay for 

 pottery purposes, but there were no sections exposed at the time 

 of my visit. The fundamental rock is here Lower Silurian, and it is 

 the only instance that has come under my observation of these de- 

 posits occurring off the Mountain Limestone. 



VOL. IV. so, XXXVI. 16 



