Wright — List of Irish Cretaceous Microzoa. 75 



weight of the material. Chalk flints are usually found hard and solid through- 

 out, only a small proportion of them having cavities containing Chalk powder. 

 So far as I have observed, those containing the powder appear to be confined 

 to flints that have, for some time, been exposed to the action of the weather, 

 the white material frequently seen in the interior of those newly quarried being 

 always of a hard nature. I have met with Chalk powder in every stage, from 

 powder as fine as the finest flour, to a material so hard that it was difficult to 

 cut it with a penknife. The flints that contain powder may be readily known 

 from the solid ones, by having openings from the outside varying much in size, 

 the only trace at times being a little moss that has taken root on the chalky 

 material exposed near the surface. It is not intended that the present list of 

 Microzoa should be considered exhaustive, our knowledge of the contents of 

 the flints in the North of Ireland is after all but very limited. Many localities 

 in the northern parts of the Counties of Antrim and Londonderry have yet to 

 be explored, whilst at several of the stations already examined the search for 

 Chalk powder has been most cursory, and on several occasions only small 

 samples of it were collected during hurried visits. 



The Cretaceous rocks of the North of Ireland are found invariably underlying 

 the Basalt, and are usually well exposed at the base of those hills which occupy 

 the boundary line between it and the sedimentary rocks. They occur as a 

 narrow belt of White Limestone and Greensand around the great basaltic 

 plateau which occupies nearly all Co. Antrim and the eastern part of Co. Derry. 

 I have given the localities for the Chalk Microzoa in the order in which they 

 occur, commencing at Magheralin, the most south-westerly point examined ; and 

 then, in a north-easterly direction, through Lisburn, Belfast, Carrickfergus, 

 Islandmagee, to Larne ; then, north and north-west, round the coast to the 

 Giant's Causeway ; then, inland, into Co. Londonderry, ending in the high 

 escarpment of Slieve Gallion and Keady Hill. 



To my friend, Prof. T. Rupert Jones, F. R. S., I am deeply indebted for 

 kind assistance rendered by him in the critical examination of my entire 

 collection of Ostracoda and Foraminifera — an examination which has resulted 

 in the detection of several new species. I am further indebted to Prof. Jones 

 for names and references respecting all the forms here enumerated. Dr. J. S. 

 Bowerbank, F.R. S., has also laid me under weighty obligations, by gener- 

 ously undertaking to revise my whole series of Sponge spicula, a work of 

 peculiar difficulty. His report on the spicula will be given in full. To my 

 friends, Mr. William Gray, M.R.I. A., Mr. Samuel A. Stewart, F.B.S.E., and 

 Mr. Thomas Galloway, I am indebted for kind and liberal assistance in 

 procuring for examination a large amount of material from various localities. 

 To the kindness and skill of my friend Mr. William Swanston I am much 

 indebted for the very accurate drawings in the plates which accompany this 

 memoir. 



