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Proceedings of tlie Royal Society of Edinburgh. [Sess. 
crystalline matrix more than is usually the case. Sponge spicules are 
common ; portions of their spicular canal are sometimes coloured by the 
brown infiltration. The whole rock must have been permeated with 
colloid silica in minutely globular form. 
3. — Section through nodule and sandstone from the hand specimen 
collected by Mr Clough. Inoceramus prisms are the chief ingredient of 
this rock, the matrix being packed with them. Foraminifera are common ; 
amongst them are Globigerina, two or three species of Textularia, and 
several Rotaline forms. Globigerinse do not predominate ; there are as 
many Textularians. Nearly all are large bold forms, well preserved and 
distinct in outline. Sponge spicules occur, but not in great numbers, and 
I am of opinion that more than one Radiolarian occurs in this section. 
The rock was at one time permeated with colloid silica. 
4. — This section is practically a continuation of No. 3 : it is chiefly 
cut through the sandstone, but includes several specks which can be seen in 
the rock. These specks are clearly the silicifled fragments of two, if not 
three, calcareous oozes laid down under different conditions of sedimenta- 
tion ; though unlike each other, they agree in general structure with the 
three nodules described above. 
These fragments of silicifled chalk preserved in the sandstone of Eigg 
are very similar to those of Argyllshire. One nodule is certainly '‘Ino- 
ceramus chalk ” (0^ 3, Beinn-y-Hattan). Other nodules are altered siliceo- 
calcareous oozes, a mixture of Foraminifera, shell fragments, and spicules, 
often permeated with colloid silica in minutely globular form. 
The border-line between the nodules and the sandstone is, as a rule, 
sharply drawn ; but in T 4603 the matrix of the chalk has penetrated and 
infilled the interstices between the sand grains for some little distance 
beyond the nodule. 
From the above it would appear that the whitish calcareous sandstone of 
Eigg, though occupying a stratigraphical position which enables it to be 
considered as a representative of the Cretaceous series in the West of 
Scotland, is in reality a sandstone containing fragments of chalk now 
silicifled from more than one horizon. 
Cretaceous limestone from volcanic neck, from Ballymichael, 6 miles 
S.W. of Brodick Bay, Arran. The ground mass is minutely crystalline 
chalcedony, but it is full of calcareous particles. The rock contains many 
shell fragments; the larger ones are practically calcitic crystals showing 
the cleavage planes, their structure being obliterated. Though a few Ino- 
ceramus prisms are present, the greater part of these fragments do not 
suggest derivation from Inoceramus. Many are large angular pieces some- 
