212 THE FLORA OF WARWICKSHIRE. 



II. "Rare — Cookkill in some boggy ground," Purt., i., 213; Packmore 



Fields, Warwick, Perry, I •'/. 40; Oversley ; Binley ; near 

 Newbold-on-Avou ; Combe Woods, &o. 

 I think that this plant must have been overlooked by Purton, as I 

 find it by no means rare in the Avon basin. 

 (To be continued.) 



HOW TO WOKK IN THE AKCH/EAN ROCKS.* 



BY C. CALLAWAY, M.A., D.SC, (lOXD.,) F.G.S. 



The Archaean (Pre-Cambrian) rocks have recently excited consider- 

 able interest, owing partly to the more or less complete working out of 

 the younger groups, and partly to the fascination which attends a 

 study of peculiar complexity. 



In America, six Archaean systems have been described, which, taken 

 in descending order, are the following :— 



I. — Keweenian, cr copper-bearing series of Lake Superior. 

 II. — Taconian. 

 TH.—Montalban,ox taica-schisfc series. 

 rV. — Huronian. 



V. — Norian. 

 VI.- — Latvrentian. 



In Britain, Murchison recognised the Laurentian in the greatgneiss 

 series of the Hebrides, and Dr. Holl claims the same antiquity for the 

 Malvern ridge. Salter and Kicks discovered two Archaean groups, 

 Dimetian and Pebidian, at St. Davids. Two Archaean formations have 

 also been recognised in Carnarvonshire, and the writer has worked 

 out two groups in Anglesey. He has also discovered two series, a 

 volcanic and a metamorphic, in Shropshire, and lias detected the 

 former on the flanks of the Malverns, The slaty and brecciated rocks 

 of Charnwood Forest have also been referred to the Archaean by Dr. 

 Hicks, subsequent to their description by Messrs. Hill and Bouney. 



Notwithstanding the peculiar difficulties attending the study of 

 these rocks, there is no reason to despair of success, and, in this paper 

 the methods of work are indicated. 



The evidence of organic remains is rarely applicable. The organic 

 nature of Eozoon is strenuously disputed, and. in the present state of 

 the controversy, the (so-called) fossil is of little value as a test of age. 

 Besides this, a similar structure lias been discovered in the Taconian. 

 and Murchison even claimed it as a Silurian fossil. The traces "I 

 annelides, which are found in some very ancient rocks, are hardly 

 distinguishable from recent tracks and burrows, and are of little classi- 

 ficatory use. 



The test of order of superposition is frequently complicated by 

 inversions. Iu North America the Arelnean rocks have a general south- 

 east dip, but really tins are made up of numerous parallel folds, with 



* Summary of a paper read before the (leologiciil Section of the Birmingham 

 Natural History and Microscopical Society, on June 28th, 1881. Published in full 

 in the " Geological Magazine." 



