572 Correspondence — Mr. O. H. Kinahan — 



from eigliteen inches on the longer axis to the size of a bean, and 

 from a spherical to an ellipsoidal figure. 



We have not far to seek for their origin, as a visit to the lower 

 edge of the peat frayed into a sort of subtidal cliff or series of cliffs 

 by the encroachments of the sea shows a deposit of similar clay 

 boulders at its base. In the neighbourhood of the trench the Eiver 

 Alt meandering over the shore has made great inroads on the Post- 

 Glacial deposits, which compose the substratum, forming a subtidal 

 river cliff of blue clay on its western margin. Lumps of this clay 

 undermined by the currents, fall, break up into pieces, and get 

 rolled into boulders by the action of the tide. The trench has 

 formed a sort of trap for catching and retaining them. The clay- 

 boulders are in contact, and become in the trench compacted 

 together into one solid mass, so that if it were converted into rock 

 its structure would show in some cases distinct argillaceous boulders 

 in a sandy argillaceous matrix, and in others an imperceptible 

 shading of the boulder nucleus into the matrix. 



Simply describing the foi'egoing facts for the information of those 

 interested, I leave geologists to apply the explanation to some of the 

 conglomerates. T. Mellakd Eeade. 



SIR RICHAED GRIFFITH AND THE OLD RED SANDSTONE. 



Sir, — The last big talk I had with the late Sir Eichard Griffith 

 was immediately before the British Association Meeting in Belfast, 

 and it was on my work in West Galway and Mayo. Previous to it 

 I had left my maps and sections with him to examine after ex- 

 plaining them. During this conversation we discussed the age 

 of the Louisburgh Toormakeady and Croogh Moyle beds which had 

 been examined and proved to be of Silurian age, and Griffith pointed 

 out that the Curlew Mountain rocks and those near Firodes he always 

 believed to be of the same age and to be about equivalent to the Diugle 

 beds, " but I never," said he, " had time to examine them carefully, 

 and I left them in the Old Eed Sandstone because they were very 

 like the conglomerates of the Comeraghs Gaiters and Knockmeal- 

 down Hills." He also pointed out that there was a decided un- 

 conformability in the rocks said to belong to the "Old Eed Sandstone 

 formation " in Ireland ; while the newer rocks so called seemed to 

 be on different geological horizons. He concluded by saying, " My 

 work must remain as it is, but the working out of the question has 

 still to be done," or words to that effect. Since then I have been 

 carefully examining into the question, starting on what was suggest- 

 ed to me by Griffith, and the results of my labours will be found in 

 my recently published Manual of Irish Geology. This is sufficient 

 to say at the present, as I hope to enter fully into the history of the 

 subject in a paper to be read before the Eoyal Geological Society of 

 Ireland. G. Henbx Kinahan. 



OvocA, Ireland, 5th November, 1878. 



