1910 GEOLOGICAL DETAILS xv 



Precedentive palingenesis. — ^This term is proposed for the phenomenon 

 of acceleration greater in one character than another, so that a feature 

 of one part which, according to the phylogenetic record, was developed 

 later than a feature of another part, is unduly accelerated, until, in 

 ontogeny of later species, it precedes instead of succeeds. Thus phylogeny 

 may show the ventral carina as a later development than lateral ribs ; 

 but ontogeny of later species may show carina appearing before ribs. 



In Man, the rapid development of the brain and enlargement of the 

 skull in the embryo would appear to be an instance of precedentive 

 palingenesis. 



Among Nautiloids the furrow due to whorl-contact (ophiocone 

 stage) appears in the ontogeny of higher forms (nautilicones) before 

 contact takes place. This is either precedentive palingenesis, as regards 

 the furrow, or cunctative palingenesis in undue retention of the cyrto- 

 cone stage. 



For principles of Ammonite development see Hy.^tt's papers in 

 Proc. Boston Soc, 1867 — 1883, and especially his Genesis Arietidae. 

 There are also remarks in the Editor's Mon. Amm., especially 1905, 

 cxcviii ; and in Schlotheimia, Proc. Cotteswold, xv, 1906, 232 ; and 

 a genealogy in Jur. Time, Quart. Journ. Geol. Soc, liv, 1898, 451. 



Geological Details (Lias) 



The Table overleaf gives the scheme of stages and zones which 

 it is proposed to adopt in the present work for recording the positions 

 of species in the so-called Lias rocks. Simpson's divisions of the York- 

 shire strata are compared, so far as is possible from his information. 

 There are some discrepancies between the statements in his sections 

 and in his descriptions, but they are unimportant. 



In this table the stratigraphical terms, zone and stage, have 

 been employed. The corresponding chronological terms, hemera and age, 

 are often more useful, particularly hemera. For a zone may contain 

 species which lived during several different hemerae, and the finding 

 of species in a certain zone is no proof of their contemporaneity. The 

 zone in which a specimen is found in the field and the actual date of 

 its existence are two different observations. 



The thickness of the Lias strata in Yorkshire is estimated by Simpson 

 to be about 800 feet ; but Tate & Blake (Yorkshire Lias, 1876, 194) 

 give reasons for making the total about 1,100 feet. 



There is a tradition among geologists, often repeated in text-books, 

 that the term " Lias " originated as a word of the Somerset quarrymen — 

 their corruption of " layers." That folk-speech is a corruption of literary 

 speech receives in this, as in many other cases, little support from philology. 

 Prof. Skeat, in his " Etymological Dictionary," says that the word lias 

 is old in French, where it appeared as " liais. Hois, : ' Liais, a very hard 

 free-stone, whereof stone-steps and tombe-stones be commonly made ; ' 

 Cot. Spelt Hois in the 13th cent. (Littre.) Perhaps from Bret, liach, 

 leach, a stone. Cf. Gael, leac, a flat stone, W. llech." 



So lias, accordmg to this account, is a form of the word which occurs 

 in place names like Llechryd, Lechlade, Lec^hampton, 'Koithleach. 



Through the Celtic custom of dropping initial p, the words llech, 

 leac, etc., are cognate with Greek 7rAa|, Latin planca : see Fick, 

 " Worterbuch," 1891. 



