220 Notices of Memoirs — Prof. King — 



and general sub-angularity in the form of these ironstone concretions,, 

 and may explain also the analogous peculiarities of many Chalk- 

 flints. These latter occur in thin plates and tabular masses following 

 lines of bedding, joints and fissures, in spheroidal and elongated 

 forms, or in a mixture of both kinds, presenting odd corners and 

 angles scarcely compatible with chemical aggregation around a 

 central nucleus. The hollow portions are frequently filled with 

 loose powdery chalk, and, except that they have not been observed in 

 actual stages of transition, the Chalk-flints present characters similar 

 to those of the Lower Greensand concretions. 



ZsTOTICIES OIF DVCZEnVCOHE^S- 



♦ 



I. — Eeport on the Supekinduced Divisional Structure of 



EOCKS, CALLED JoiNTING ; AND ITS EeLATION TO SlATY ClEAVAGE. 



By William King, Sc.D., Professor of Mineralogy and Geology, 

 Queen's University in Ireland, and Queen's College, Galway. 

 Being Article XX. of Vol. XXY. (Science) of the Transactions 

 of the Eoyal Irish Academy, 4to., pp. 605-662, plates 34-38, 

 (Dublin, 1875.) 



THE "Character of Jointing" is first treated of (pp. 606-612), 

 several examples being mentioned ; the " cleat " of coal, chert,, 

 and other rocks, and especially of the coaly cuticle of Lepidodendron 

 and other fossil plants, is taken as a familiar instance, and is regarded 

 by the author as the analogue of mineral cleavage rather than of the 

 prismatic jointing of basalt. Further examples of rock -jointing are 

 referred to in the treatment of the "Extensions of Jointing" 

 (pp. 612-618). The shifting, or dislocation of jointings in some 

 beds which have been vertically jointed, among others destitute of 

 divisional planes, is described in detail (pp. 620-626), with 

 examples. "Jointing developed in diff'erent Geological Periods," 

 and " The Origin of Jointing," occupy pages 626-642 ; and Part II., 

 " Jointing in its relation to Slaty Cleavage," with some notes, con- 

 cludes the Memoir. A lithographic view of a wide area of bare 

 jointed limestone, on the south side of Galway Bay (pi. 34), and 

 numerous diagrams of the stratal conditions referred to (pis. 35-38),. 

 illustrate the Memoir. 



The author alludes to the former promulgation of his views on the- 

 relation of joints and cleavage, in 1857-8 ; and now treats of his 

 further researches, in which he has been aided by a grant from the 

 Eoyal Irish Academy. Observations and opinions of others on the 

 interesting subjects of jointing and cleavage are carefully alluded to, 

 and often given in full. 



In this Memoir, Prof. W. King, of Galway, urges the existence 

 of universally distributed divisional planes, or joints, in a great 

 variety of rocks constituting the earth's surface. He regards the 

 joints as having been originally, and still often remaining, vertical ; 

 and as having either a more or less "meridional," ^ or a more or less 



1 Spelt " meridianal " throughout in the original; hut this modification, like 

 " stratial" also throughout the memoii-, we regard as neither necessary nor correct. 



