Relations of the Secondary Strata in the Isle of Arran. 25 



with layers of remarkably fine red sandstone. It is unnecessary to describe 

 these beds in very great detail ; many of them resemble the harder varieties 

 of the new red sandstone of England, and exhibit a blotched and varie^-ated 

 character. Some of the conglomerates contain an extraordinary number of 

 white quartz pebbles of various sizes, the presence of which can hardly be 

 explained by the degradation of any of the neighbouring rocks ; other beds 

 of this conglomerate are, on the contrary, and agreeably to the general 

 analogy of similar rocks in other parts of Scotland, made up of fragments de- 

 rived from the neighbouring slate series. We did not remark any granite 

 pebbles in the conglomerate, — an important fact, first noticed, we believe, 

 by Dr. MacCulloch. Among the conglomerates were some in which the 

 fragments were so far comminuted as to resemble coarse white sand- 

 stone ; in other beds the pebbles were held together by a pure white calca- 

 reous cement. If the specimens were described at great length, it would be 

 necessary to mention the different colours of the strata, arising from the va- 

 rieties of the imbedded pebbles and the change of the cementing principle : 

 on the whole, however, a red colour characterized both the conglomerate and 

 sandstone. By reference to the coast section *, it will be seen that this group 

 is superior to the formations about to be described ; from which we infer that 

 it must represent the new red sandstone of English geologists. 



The preceding group is succeeded by a set of beds of considerable thickness, 

 partaking of the same dip to the N. W. and exhibiting a character intermediate 

 between the new red sandstone and the carboniferous series ; the upper por- 

 tion composed of red and gray variegated blotchy marls, alternating with soft 

 white freestone, singularly meagre and harsh to the touch. Iron-stone nodules 

 are interspersed among these beds, some of which have that false cleavage so 

 characteristic of portions of the new red sandstone. Towards the bottom of 

 this series the white freestone predominates, and gradually passes into sand- 

 stone and grits, apparently belonging to the upper part of the coal-measures. 

 This intermediate group of the series is extended for a few hundred yards 

 along the shore, and is terminated by six or eight thin beds of compact red 

 limestone containing organic remains, which are of great importance in de- 

 termining the true relations of the Arran secondary strata, and have not been 

 noticed in any previous account of the structure of this island. The highest 

 of these beds are of a deep red colour, thin and fissile, resembling an indurated 

 calcareous shale, and contain numerous organic remains standing out in relief, 



* Plate III. 



VOL. III. SECOND SERIES. E 



