J.VM1ES0N CRAG, ABERDEENSHIRE. 373 



for, as flints are common in these beds, itwouldshow that they could 

 not have been drifted hither during the glacial period, but must have 

 existed in the district before. 



In addition to the flints, these so-called Crag beds contain great 

 quantities of limestone-fragments, apparently derived from secondary 

 strata, and unlike any rock I have seen hereabouts. Some of them 

 are of a yellow, others of a smoke-grey colour ; they are of a tough, 

 compact, earthy texture, and often finely laminated. Organic remains 

 are rare in them, but do occur. A day or two ago I struck open a 

 cast of a Terebratula in one, and a small elongated species of Mytilus, 

 and have seen the impression of a little Fish in another. The aspect 

 of the Terebratula suggests a Permian age ; and the general character 

 of the fragments altogether seems to resemble that of the Magnesias 

 limestone. ^Yhcre they came from, however, is a mystery. 



There arc also many fragments of red and grey sandstones — all 

 whispering, as it were, of some great denudation that has taken place 

 in the suiTounding region. 



P.S. [September 24t7i, I860.] — Since the above was written, Mr. 

 Searlcs Wood, whose monograph on the Mollusca of the Crag has 

 associated his name so indissolubly with that subject, has done me 

 the favour of examining the fragments which I had collected from 

 these beds. He agrees with me in thinking that, altogether, they 

 have decidedly a " Crag" aspect ; and, " on the whole," he says, 

 " I think you arc justified in assuming that the Red Crag sea ex- 

 tended itself into your neighbourhood." 



Mr. Wood has also identified the following additions to the above 

 list of Mollusca : — 



Nassa reticosa, var. rugosa. " A truly characteristic fossil of the 



Eed Crag." 

 Pholas. Several fragments. 

 Glycimeris ? Two fragments. 



I would tain Bay a word or two as to the probable cause of the 

 .preservation of this patch of Crag; for the thickness of the mass 

 showB it to be the remnant of a more widely spread deposit ; and it 

 Lb remarkable that not a trace of it is seen in the adjoining valley of 

 theYthan. Then- must, therefore, have been some peculiar reason 

 why it was left here only and nowhere else. Now, I have fre- 

 quently remarked that the locality is one that during b glacial epoch 

 would be singularly out of the way of the movement of land-ia 

 under the most frigid climate that could be supposed, and one also 

 remarkably secure from the destructive effects of off-rushing water 

 during movements of upheaval. I cannot, therefore, avoid thinking 

 that its preservation may have been due to this favourable position 

 during the vicissitudes of the Drift -period. 



