230 . Rcvieivs — E. Kidston's Memoirs. 



in resisting the south-easterly thrust to which these structures are 

 due, and that it has even operated in the formation of the phyllites 

 of the " Llanberis slate zone," while it has sheltered the region to 

 the north-west from cleavage and intrusion. The western district, 

 being less affected and not possessing a resisting mass, has lagged 

 behind the eastern, so that faulting and dynamic changes in the 

 diabases have taken place about the junction region of Tremadoc. 

 The foci of the main eruptions bear a relation to this thrust, and 

 are found along a line to the south-east of, and parallel to, the Lbyn 

 Padarn ridge, indicating that the thrusting had begun before the 

 vulcanicity. 



The eruptive material, if of intermediate character to begin with, 

 seems to have segregated before eruption occurred, so that the lavas 

 are of acid character ; the diabases on the other hand, owing to their 

 density, were intruded as sills at lower levels, possibly in part during 

 the main vulcanicity, but also and chiefly after the surface flows 

 ceased ; still later and lower are found the ultrabasic intrusions. 



In this work we have a very large amount of observation and 

 inference which will form a most useful groundwork when the 

 district is studied minutely and mapped in detail, and then only can 

 its deeper and more complicated problems be unravelled. — W. W. W. 



III.— Memoirs by Eobert Kidston, F.B.S.E., F.G.S, 



1. On the Fossil Plants in the Eavenhead Collection in the 



Free Library and Museum, Liverpool. Trans. Eoyal Soc. 

 Edinburgh, 1889, vol. xxxv. pp. 391-417, pis. i. ii. 



2. On some Fossil Plants from Teilia Quarry, Gwaenysgor, 

 near Prestatyn, Flintshire. Trans. Eoyal Soc. Edinburgh, 

 1889, vol. xxxv. pp. 419-428, pis. i. ii. 



3. Additional Notes on some British Carboniferous Lycopods. 

 Ann. Mag. Nat. Hist. 1889, pp. 60-67, pi. iv. 



THESE Memoirs form valuable additions to the literature of our 

 British Palaeozoic. Flora. The report on the "Eavenhead Col- 

 lection " is prefaced by a geological sketch of the district from the 

 pen of Mr. G. H. Morton, author of the " Geology of the Country 

 around Liverpool," the plants described having been collected in 

 the Middle Coal-measures at Eavenhead, near St. Helen's, South 

 Lancashire. The species referred to belong to the groups of the 

 Calamarice, SphenopliyUete, Fih'cacece, Lycopodiacete, etc., Sphenopteri s 

 Marratii being described as a new form, whilst Stur's genus 

 Spliyropteris (a Sphenopteroid fern) appears to be recorded for the 

 first time from British rocks. The occurrence of Zeilleria delicatula 

 is also mentioned. Unfortunately this genus established by the 

 author in 1884 must, in accordance with the laws of priority, be 

 dispensed with, that name having been applied by Prof. E. Bayle 

 in 1878 to a genus of Brachiopods. 



The Teilia Quarry plants are from the Carboniferous Limestone, 

 and an interesting fact connected with them is their association with 



