290 



NATURE 



{Jtily 28, 1887 



attention also to the bearing such considerations have on 

 the attempts which are occasionally made after minute 

 correlations and identifications of individual beds in such 

 a group of strata. The example set in this matter in the 

 present work is excellent, for a clear distinction is drawn 

 between those limestones or other beds about whose con- 

 tinuity there can be no question, and those whose occur- 

 rence is local ; but example may be usefully enforced by 

 precept. 



The same wholesome refusal to draw hard and fast 

 lines where none have been drawn by Nature is seen 

 when we come to the chapter on the Tuedian beds. 

 Special attention is drawn to the fact that, though these 

 can be separated, as far as lithological character goes, 

 from the overlying Bernicians, the line of demarcation is 

 by no means everywhere of the same geological age. 

 The Tuedian beds resemble so closely the " Cement 

 Stone Group " of the central valley of Scotland, that they 

 are doubtless the southern continuation of that sub- 

 division. The Scotch beds, as is well known, were laid 

 down in an assemblage of ponds, creeks, and lagoons 

 separated by banks of sand and muddy shoals. The 

 Tuedians of the north of England do not seem to show 

 quite such rapid changes horizontally as are common in 

 their Scotch equivalents, but they must have been formed 

 under very similar conditions. Beds thoroughly Tuedian 

 in character occur on the west of the Cross Fell Range 

 near Shap ; they are very thin, and we are there probably 

 close to the southern boundary of the area over which 

 these peculiar beds were laid down. 



Very interesting are the accounts of the somewhat 

 peculiar group of rocks discovered in the deep borings 

 for rock salt alongside the Tees. First came more than 

 1000 feet of Red Marls and Sandstones, which may be 

 very safely assigned to the Trias. Judging by what is 

 seen at the outcrop, we should have expected the main 

 mass of the Magnesian Limestone to follow ; but such 

 was not the case. The hole then entered a group of 

 rocks consisting of gypsum, anhydrite, rock salt, and 

 beds of limestone. Prof. Lebour is of opinion that the 

 Magnesian Limestone was not reached by any of the holes. 

 Hereby several questions may be started. Are the 1000 

 feet of red marl and sandstones to be assigned to the Red 

 Marl or the Red Sandstone ? A nice difficulty for the 

 system- mongers ; but before we try to solve it, we may 

 ask \\helher these two subdivisions are as sharply 

 marked off from each other in Yorkshire and Durham as 

 in other parts of England. There is no reason why they 

 should be ; and if they are not, we may well content our- 

 selves with calling the whole Trias. Then how are we to 

 account for the presence of the rock salt and gypsum, 

 which, as far as is known, is never seen along the outcrop, 

 or indeed anywhere else in England ? It seems likely 

 that towards the end of the Permian period unequal sub- 

 sidence produced hereabouts a depression in the bed of 

 the water ; that, as now happens elsewhere under similar 

 conditions, the Permian lake became largely laid dry, so 

 that water remained only in this and perhaps other 

 similar basins ; and that, from the highly concentrated 

 solutions which remained in these lakelets, local deposits 

 of a strongly chemical character were precipitated. The 

 author remarks on the close resemblance which these 

 deposits bear to the subdivision of the Permian called 



" Rauchwacke " in Germany, and would apply this name to 

 them. That they and the German " Rauchwacke" were 

 formed under very similar conditions there can be little 

 doubt, but there is no proof that the two were formed at 

 the same time, and this is almost necessarily implied if we 

 give them the same name. In a group of rocks like the 

 Permian, formed in so many distinct basins, and under 

 changing conditions the order and nature of which were 

 probably never the same in any two basins, the minor 

 subdivisions must necessarily be totaUy different in 

 different areas, and any attempt to correlate these minor 

 subdivisions can be little better than guess-work. If the 

 subdivisions are to have distinctive names, it seems 

 better that the beds of each basin should each have a set 

 of names to itself. Similar objections apply to the habit 

 of designating the subdivisions of the English New Red 

 Sandstone by German names ; it is the practice to look 

 upon the New Red Marl as the time-equivalent of the 

 Keuper, and the New Red Sandstone as that of the 

 Bunter, but there is absolutely no proof of this. It is 

 worse when a statement is made that .the Muschelkalk is 

 absent in England, and a fictitious unconformity is postu- 

 lated between the New Red Marl and the New Red 

 Sandstone to account for its absence. Who can say 

 whether the lower part of the New Red Marl, or the 

 upper part of the New Red Sandstone, or both, were 

 not forming here while the Muschelkalk was being 

 deposited in Germany t 



The peculiarities of structure exhibited by the Mag- 

 nesian Limestone are shortly but cleai-ly described. They 

 have been long known^ but little has been done towards 

 explaining how they were produced. The problem is 

 one of extreme complexity, but a persevering attack on it, 

 even if it did not lead to a complete solution, would 

 almost certainly throw great hght on what we in our 

 ignorance call concretionary action. Sundry structures, 

 formerly referred to this mysterious cause, have been 

 shown to be due to simpler and less recondite processes, 

 but there is a large residuum of cases still awaiting 

 explanation. 



We have by no means exhausted all the questions and 

 suggestions which this little book will prompt ; but we 

 hope we have said enough to show that it will prove to 

 the attentive reader far more interesting than might at 

 first be supposed. And we may learn from it that in 

 Great Britain, the very motherland of geology proper, 

 ransacked as it has been for now well-nigh a century by 

 the ablest of geologists, there is still many a corner, full 

 of unsolved problems, awaiting the attention of those 

 geologists who cannot wander far from home but are yet 

 anxious to win their spurs. 



A. H. Green 



PHYSIOLOGICAL PSYCHOLOGY. 

 Elements of Physiological Psychology. A Treatise on ti 

 Activities and Nature of the Mind from the Physi 

 and Experimental Point of View. By George T. Ladd, 

 Professor of Philosophy in Yale University. (London : 

 Longmans, Green, and Co., 1887.) 



THE aim of this volume is twofold : first, to giveB 

 clear, accurate, and up-to-date account of tW| 

 psycho-physiology of man ; and then to enter a pro- 



t 



