Notices of Memoirs— J. R. Bahijns—Fekitic Lam. 79 



Another interesting feature, not before noticed in the Lower 

 Limestones, is the mass of incrusting organisms. These organisms 

 formed a crust around the fragmental remains of other bodies 

 which collected on the sea-floor, and to such an extent did this 

 process go on that the incrusting organisms contribute considerably 

 to the building up of some beds of limestone. Whether these crusts 

 are to be attributed to animal or vegetable growth is a matter 

 of doubt. 



The crinoidal life reached a climax during the time that the Black 

 Kock Limestone was in process of formation. Indeed, this rock 

 is, in the main, a vast accumulation of the ossicles of these " stone- 

 lilies." associated with shells of mollusca, fish remains, etc. 



The Black Rock series terminate in dolomitized limestone, and on 

 this rest the ' Gully Oolites.' 



The Lower Limestones terminate at these oolites, in which occur, 

 though sparingly, foraminifera and the minute spherical ^ object 

 Calcisflimra. This latter body averages about -012 of an inch in 

 diameter, but, small as it is, the calcareous sphere has been an 

 important contributor to the building of the rocks. 



As Calcisphcera is confined to the Carboniferous Limestone, and is 

 so numerous that it is seldom a thin section of the rock is obtained 

 without finding it, the organism is useful in determining the strata 

 when doubtful. So far, the author has not found Calcisphoira in the 

 Lower Limestones, and the same remark applies to foraminifera. 



Above the horizon of the Gully Oolite the lower beds of the 

 Middle Limestone are characterized by the occurrence of the curious 

 organism Mitcheldeania, but it is not confined to this horizon. 



Next follow limestones and calcareous shales full of the remains of 

 little understood forms of microscopic life, which must have existed 

 in gi'eat profusion. 



As before remarked, the Middle Limestones are characterized by 

 foraminifera and Calcisphcera. At first these occur sparingly, but 

 later on the rock is little more than a Carboniferous foraminiferal 

 ooze. Eemains of corals occur and other well-known fossils, but the 

 bulk of the 1,600 feet of limestone included in the Middle Series is 

 in the main a vast calcareous deposit of the remains of microscopic 

 life which lived in the Carboniferous waters. 



Owing to the Upper Limestones being so built over, the author is 

 at present not in a position to describe the microscopic life which the 

 strata probably contain associated with larger organisms. 



YIL — On the pkobable Source of the Upper, Felsitic Lava 

 OF Snowdon.^ By J. R. Dakyns, M.A. 



BETWEEN Glaslyn and Bwlch Goch, as the lowest part of the 

 ridge between Crib Goch and the top of Crib y Ddysgl is 

 called, a mass of felstone rises like a wall through the beds of the 

 calcareous a&hy series. The trend of the dyke is E.N.E. The best 

 section is along the N.W. face, where the felstone is clearly seen 

 standing as a wall against the truncated edges of the calcareous 

 1 Eead before Sect. C (Geology), British Association, Bristol Meeting, Sept. 1898. 



