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HARDWICKE'S SCIENCE-GOSSIP. 



[Oct. 1, 1870. 



hardly a space of a pin's point which is not occupied 

 by the remains of some creature in which the breath 

 of life was enjoyed countless millions of years ago ! 

 You strike the solid rock with your hammer, and 

 immediately the percussion liberates a heavy sul- 

 phuretted odour, wbich tells of the old animal 

 gases in which the limestone is steeped. The very 

 hardness of these rocks is more or less indebted to 

 the same orgauic cause. I am told that when 

 sculptors, nowadays, wish to harden their plaster 

 of Paris casts, they do so by boiling them in oil. 

 The principle is the same with most limestone rocks 

 of every age. They are steeped, saturated in 

 animal oils; nay, in many places across the Atlantic, 

 where these old Silurian limestones and shales lie 

 so deep down as to be within the action of the 

 earth's internal heat, these oils have been distilled 

 out of the rocks, and have followed the ordinary 

 habits of fluids. It is by sinking through the over- 

 lying masses that these oil-springs are reached, and 

 the valued liquor comes bubbling to the surface. 

 Well does it deserve its common name of Petroleum 

 —"rock-oil." 



But few people imagine, when its brilliant light is 

 illuminating their comfortable homes, that they are 

 indebted to distilled Trilobites for the luxury ! Here 

 is another form of that grand law of correlation of 

 physical force. The ancient Silurian sunlight fur- 

 nished the means of vitality to the creatures which 

 then enjoyed life. It was stored up in their tissues, 

 and given forth in their buoyant gambols and locomo- 

 tive powers. And when they died, what remained in 

 their diminutive bodies decomposed, passed into 

 other chemical forms, was preserved until our own 

 day, when men uulock this ancient sunlight from 

 its oleaginous condition, and turn it to direct heat- 

 ing and lighting account ! Fancy sunlight bottled 

 up in form of trilobites and mollusca ! No wonder 

 these should present such stony and petrified ap- 

 pearances, when all the animal oils have been so 

 completely drained out of them. 



How long these Wenlock limestones (for that is 

 the name by which this section of the Silurian for- 

 mation is known),— how long, I say, it is since these 

 limestones were upheaved and exposed to the ac- 

 tion of the weather, I cannot say. Their hardness, 

 I have already mentioned, is most intense ; but the 

 wear-and-tear of the atmosphere has been such as 

 to cause the fossils to stand out in relief ; and a 

 strange sight, therefore, is the exposed surface of 

 a limestone slab. The eye is bewildered by the 

 number and variety of orgauic remains, each 

 standing forth from the fine limy mud in which it 

 was originally enclosed. Little or no vegetation 

 grows on this bare limestone surface; the latter is 

 too impenetrable to yield a foothold ; and so the 

 geologist has it all to himself. Heads and tails of 

 Trilobites, so plentifully dispersed that they imme- 

 diately stamp the Silurian age of the rock, lie com- 



mingled with brachiopodous shells, worm-tubes, 

 sea-mats, chain -corals, and encrinite stems. You 

 require no prompter to remind you of the exuber- 

 ance of animal marine life in this distant epoch, 

 and yet the Silurian period immediately succeeds 

 the Cambrian, about which my distant relative, the 

 Piece of Slate, gave you an account some time ago. 

 Whilst the limy mud — which subsequently be- 

 came hardened into solid rock, and then upheaved 

 into its present condition— was being slowly formed 

 in deeper water, nearer to the shore there were 

 deposits of a different nature going on : these con- 

 sisted of muds poured into the sea by rivers, or 

 wasted by tidal and current action from old coast- 

 lines ; gradually, therefore, the limy deposits 

 passed into the muddy ones, so that the line of 

 junction was almost imperceptible. Occasionally 

 the fine mud was carried further seawards than 

 usual, and then a thin layer of argillaceous matter 

 was thrown down over the limy material. This 

 accounts for the frequent alternations of limestone 

 bands and argillaceous shales which you have 

 doubtless seen in every section of Silurian strata. 

 At various epochs during the immensely long 

 period which elapsed whilst these beds were form- 

 ing, alterations of the sea-bottom took place ; the 

 area where limy deposits had been forming became 

 shallow, so that clay or mud began to accumulate 

 over the same spot ; or, the sea-bottom became 

 deeper, and, in that case, calcareous or limy 

 material slowly formed where mud had previously 

 been accumulating. Occasionally, perhaps, the sea 

 became so shallow that shingle-beds were strewn 

 over the area where both lime and mud had been 

 collecting. My hearers can readily understand 

 operations like these ; they are still going on over 

 various parts of the earth's surface ; but the time 

 of observation has not been extensive enough to see 

 what they can effect. Only that simple element of 

 time is required— and our planet is changed as by 

 the will of some powerful magician ! Aud, for my 

 own part, I do not see why the timid, unconceding 

 spirit of modern times should begrudge time to the 

 geologist, any more than they do distance to the 

 astronomer ! 



The various strata which vertically succeed each 

 other in the Silurian formation plainly indicate the 

 geographical changes which affected these ancient 

 seas ; and, at the same time, imply the vast lapse 

 of time during which they were brought about. 

 Suffice it to say, this Silurian formation, with its 

 enclosed strata, attains a total thickness of no less 

 than twenty-six thousand feet ! 



Leaving my junior brethren to speak for them- 

 selves when their turn comes, let me try and re- 

 member some of the physical circumstances which 

 marked the epoch of my own birth. First of ail, 

 what a different geography marked the surface of 

 the globe then to what there is at present ! I 



