248 



HARDWICKE'S SCIENCE-GOSSIP. 



the Lower Laurentians. It consists of masses of 

 orthoclase gneiss, quartzites, crystalline limestones, 

 and anortholites, of which the last-named rock may- 

 be looked upon as a characteristic, no evidence of such 

 occurring in the lower series having been obtained; 

 while there is a strong reason to believe they are 

 similar to the norites of Scandinavia, and the 

 hypersthenites of Skye. 



The thickness of this group has been estimated at 

 10,000 feet. 



This was the state of knowledge with respect to 

 the Pre-Cambrians some twenty years since, and 

 consequently our text-books only give scanty descrip- 

 tions of the series ; but latterly investigators have 

 devoted a great deal of attention to this important 

 study, and now we may say the series is understood, 

 at least in one district, viz. that of North America, 

 owing not only to able workers, but also to its mag- 

 nificent development in that area. But, unfortunately, 

 the results arrived at are only to be obtained by the 

 perusal of a large number of monographs and pro- 

 ceedings of scientific societies. The writer therefore 

 has thought he might bestow a benefit upon the 

 student by collecting the many results and reducing 

 them to a form in which they can the better be placed 

 at the disposal of the reader, who has no spare time 

 for such research. He would at the same time remind 

 the reader that each day brings forth new light upon 

 the subject, and therefore what follows must be taken 

 with the discrimination that the true scientist always 

 exercises while engaged on the study of any new 

 matter. 



After Logan, many transatlantic geologists gave 

 their attention to this new series, to which Professor 

 Dawson applied the name Eozoic on the ground that 

 it represented a period of time greater than the 

 Palaeozoic and Neozoic together. Professors Hunt, 

 Emmons, and Hall deserve mention as perhaps those 

 to whom we owe the greater part of knowledge, and 

 their work has gone a step beyond that of Logan, for 

 it has produced indisputable evidence that the Eozoic 

 period is not composed of two systems, but rather of 

 four, so that now we must divide our table of 

 stratified rocks somewhat as follows : — 



Tabic of Geological Systems. 



Quaternary 



Neozoic 



'Tertiary 



or 

 Cainozoic 



Ule 



Palaeozoic 



/Recent. 

 1. Pleistocene. 



i Pliocene. 

 Miocene. 

 Oligocene. 

 Eocene. 

 [Cretaceous. 

 Neocanian. 

 Oolite . . 

 Lias . 

 [Trias . . 

 'Permian 

 I Carboniferous. 

 Old Red Sandstone and Devonian. 

 Silurian. 

 (Cambrian. 

 ' Montalbian. 



jjurassic. 

 JPoikilitic. 



Eozoic Huronian. 



J Norian. 

 I Laurentian. 



It will be better for the present to confine our 

 study to the American types, for more is known of 

 that series than of the European ; we shall then 

 be more capable of correlating our own series. 



Commencing, then, with the oldest system, viz. the 

 Laurentian. The name is applied, on account of 

 the presence of the group in the basin of the St. 

 Lawrence. (The river received its name owing to its 

 discoverers having arrived in the country on the 

 day of the festival of St. Lawrence.) 



Nature of flocks. — The prevailing rock is a 

 massive gneiss of a reddish or greyish colour, sparingly 

 micaceous, but often hornblendic, the latter mineral 

 being in such preponderance as in parts to make the 

 mass look more like hornblende rock. 



The gneisses are often distinctly stratified, but in 

 other cases they look more like granites, and have 

 been so named ; a negative characteristic of the series 

 is the total absence of chloritic, argillaceous and 

 micaceous schists. 



Large quantities of limestone are present, Logan 

 having made out three distinct beds of from 1000 to 

 1500 feet in thickness, which are coarsely crystalline 

 and often magnesic (it is in these masses that Eozoon 

 occurs), abounding in foreign minerals as augite, 

 hornblende, serpentine, biotite, and graphite, all of 

 which are either scattered in the beds or with other 

 minerals occur in veins and endogenous masses. There 

 are also large veins of quartz rock which are often 

 garnetiferous. 



Thickness of beds. — The total thickness of the 

 Laurentians may be taken at 17,000 feet. 



Localities. — The Laurentians occur along the At- 

 lantic belt over large areas of Newfoundland, New 

 England, and North Connecticut, on the high ground 

 of the Hudson, and the Welsh Mountains in Pennsyl- 

 vania, near Richmond in Virginia, the Iron Mountains 

 in North Carolina, round Lake Superior, in the 

 Rocky Mountains, and in parts of the Colorado range. 



Norian. — The name is applied from the great 

 development of this series of rocks in Norway. 

 They are separated from the Laurentian by an 

 unconformity. 



The rocks are rich in anorthic felspar (norite) at 

 times accompanied by small portions of hornblende and 

 augite or hypersthene, in which case the rocks pass 

 into hypersthenites ; epidote, biotite, and limonite are 

 also plentiful. They have a foliated appearance like 

 gneiss. 



The best example of these rocks is found in the 

 isle of Hitteren in Norway, we will therefore take 

 them as one type. Here they vary in structure from 

 coarse-grained and crystalline to very fine grained 

 and compact, the colour passing from a flesh-pink 

 through bluish-lavender, smoky-blue to almost black. 

 The whole series is rich in titaniferous iron ore. 



Thickness. — Dr. Henry Hunt gives their thickness 

 of from 10,000 to 12,000 feet. 



Localities. — Essex county, New York, North, Mon- 



