332 Reports & Proceedings — Geological Society of London. 



important part played in its formation by the calcareous alga 

 Solenopora (of which a new species is described), the deposit 

 constituting by far the most striking development of algal limestone 

 yet recorded from British rocks. The limestone represents a reef 

 facies of the normal Woolhope Limestone, being largely composed 

 of Bryozoa and calcareous Algae. Corals, although present, play 

 only a subordinate part. The reef appears to have grown round 

 a subsiding peniusula of Archaean rock, which evidently then 

 formed the south-western continuation of the Longmynd range. 

 The same reef facies is also found to occur at Nash Scar, three miles 

 away to the north-east, where it rests on the Upper Llandovery 

 Sandstone. The sudden change to the normal type of Woolhope 

 Limestone at Corton, near Presteign, appears to mark the northern 

 limit of this lagoon phase. 



The paper concludes with an account of the movements that 

 have taken place in the district, to which its general Caledonian 

 trend is due. 



2. " Correlation of Jurassic Chronology." Bv S. S. Buckman, 

 F.G.S. 



This paper owes its inception to certain discoveries made by the 

 Officers of the Scottish Geological Survey during their investigations 

 of the Jurassic deposits of the Isles of Baasay and Skye. The 

 Ammonites and Brachiopods were sent to the author for examination, 

 and the sequence of faunas which they disclosed necessarily led to 

 comparison with results obtained in other areas — with Yorkshire, 

 on which the author had recently written a palaeontological chapter 

 for a Geological Survey memoir, based largely on information and 

 specimens submitted by the Survey ; with the Dorset coast, helped 

 by Mr. "\Y. D. Lang's most painstaking work; with other areas 

 within the author's field experience, helped largely by information 

 most freely communicated by Mr. J. W. Tutcher. The results appeared 

 to be so far-reaching that permission was asked of the Director of 

 H.M. Geological Survey to lay before the Society a synopsis of the 

 information obtained through the investigations of Survey Officers ; 

 this was kindly accorded, and the present paper is the outcome of 

 research thus originated. 



One of the principles utilized in this paper to ascertain or to 

 surmise faunal sequence where precise information is defective, is 

 that of what maybe called "faunal dissimilarity" — that is, if the 

 deposits of two neighbouring localities A and B, supposedly 

 isochronous from their sequential position, show differing faunas, it 

 is a reasonable inference that the faunas are not of the same date. 

 Theoretical stratigraphical correlation has usually worked along 

 these lines, but the principle involved has not been recognized by 

 name. Now the principle is utilized, not only in regard to neigh- 

 bouring localities, but even more widely, with suggestive results. 



The paper is chiefly concerned with the Liassic Ages hitherto 

 known as Domerian, Charmouthian, Sinemurian. In all of them 

 there is proposed a considerable increase of the number of faunal 

 "horizons indicative of consecutive time-intervals, or hemerae. In 

 the case of the first no change of name is made ; but in regard to 



