Geological Society of London. 39 



chiefly made up of anortholite rocks, granitoid or gneissoid in 

 texture, with some true gneisses. The Huronian is seen to rest un- 

 couformably on the Laurentian, fragments of which abound in the 

 Huronian conglomerates. To the lower portion of the Huronian 

 the speaker had formerly referred a great series of petrosilex or 

 hiilleflinta rocks, described as inchoate gneisses, passing into petro- 

 silex-porphyries, occasionally interstratified with qnartzites. This 

 series, in many places wanting both in Europe and America, he is 

 now satisfied forms an imderlying unconformable group — the Arvo- 

 nian of Hicks. Above the Huronian is the great Montalban series, 

 consisting of grey tender gneisses and quartzose-schists, both 

 abounding in muscovite, occasionally with hornblendic rocks. The 

 Pebidian of Hicks includes both the Huronian and the Montalban, 

 to which latter belong, according to the speaker, certain gneisses 

 and mica-schists both in Scotland and in Ireland, as he had many 

 years since pointed out. In some parts of North America he found, 

 the Montalban resting unconformably on Laurentian. Above the 

 Montalban comes the Taconian (Lower Taconic of Emmons), a 

 series of quartzites and soft micaceous schists, with dolomites and 

 marbles. All these various series are older than the Lower 

 Cambrian (Menevian) strata of North America ; and. it may bo 

 added that the Keweenian or great copper-bearing series of Lake 

 Superior there occupies a position between the Montalban and the 

 Cambrian. 



In the Alps the speaker recognizes the Laurentian, Huronian, and 

 Montalban, all of which he has lately seen in the Biellese, at the 

 foot of Mount Viso, in Piedmont. The Huronian is the great pietre 

 verdi group of the Italians, and much of what has been called 

 altered Trias in this region is, in his opinion, probably Taconian. 

 The Montalban forms the southern slope of Mont St. Gothard, and 

 is the muscovite gneiss and mica-schist of the Saxon Erzgebirge. 

 Here Dr. Credner and his assistants of the Geological Survey have 

 described abundant conglomerates holding pebbles of Laurentian 

 rocks imbedded in the Upper or Montalban gneiss. The pre- 

 Cambrian age of this has been shown by Credner, who has proved 

 hj careful survey that the so-called younger or Palaeozoic gneisses of 

 Naumann are really but a continuous part of the older series. Late 

 surveys also show that the crj'stalline rocks of the Tauniis are 

 really Eozoic, and not, as formerly maintained, Devonian in age. 



The speaker insisted upon the fact that where newer strata are 

 in unconformable contact with older ones, the effect of lateral move- 

 ments of compression, involving the two series, is generally to cause 

 the newer and more yielding strata to dip towards and even beneath 

 the edges of the older rock, a result due to folds, often with inver- 

 sion, sometimes passing into faults. This phenomenon throws much 

 light on the supposed recency of many crystalline schists. 



The following communications were read : — 



1. " Additional Evidence on the Land Plants from the Pen-y-glog 

 Slate-quarry, near Corwen." By Henry Hicks, Esq., M.D., P.G.S. 



The author stated that since the date of his former paper (Quart. 



