GEOLOGY. 



rocks come to the surface, they are said to crop 

 out, and the exposed edge is therefore termed the 

 outcrop, as M ; the angle at which they are inclined 

 is called the dip of the rocks, and is measured by 

 the number of degrees from the horizontal in any 

 direction, as 60 S. ; and the line of the outcrop 

 along the surface is termed the strike or line of 

 strike, because it strikes or runs across the country. 

 "When the strata are not straight, they are said to 

 be bent or curved; and when greatly bent, twisted 

 or contorted, as P. When all the strata in a series 

 lie at the same angle, they are called conformable; 

 when at different angles, unconformable, as at A. 

 Sometimes certain strata seem to have slipped down 

 or to have moved up, so that rocks that should be 

 opposite to one another are not so. The portion 

 that has slipped is naturally termed a slip, as C ; 

 that which has been heaved up, an upheaval or 

 hitch : where the strata at the slip lie at different 

 angles, the slip is called a fault, as O. All such 

 displacements of strata are known as dislocations, 

 and they are much more frequent than the regular 

 disposition of rocks on the surface of the earth. 

 'Below is a good example of such dislocations in 

 coal strata, where they are abundant. The slips are 

 marked d; a dike, of trap, e; a, b, c, shew the strata 

 that have been torn up ; the dark bars are coal 

 seams. When strata are bent in wavelike undula- 



Dislocations of Coal Strata. 



tions, they are said to roll, as H ; and the hollow 

 or concave portions are termed troughs or basins, 

 and the elevated portions ridges, as I and K. 



2. Unstratified Rocks. These rocks are thrown 

 up amidst the stratified, and assume different 

 positions according to the manner of their up- 

 heaval. Where they throw the strata into various 

 angles, the rock upheaved is termed the dis- 

 rupting mass, as V ; at other times, they overlie 

 the other rocks, and are then called overlying, as 

 E ; they are also interjected between the other 

 strata, and are said to be interstratified, as F. 

 Sometimes they intersect the other strata by 

 masses like walls, which are called dikes, as G ; 

 and sometimes the disrupting mass breaks into 

 branches, which are called veins, as N. 



When a broad face of rock is exposed, and the 

 different rocks shewn, as in a cliff on the sea- 

 shore, a railway-cutting, or a quarry, such ex- 

 hibitions of strata are called sections ; and these 

 may be delineated on paper. Sections of the 

 underlying rocks may also be made, by examining 

 the different rocks in a country, though no section 

 be exposed in nature. 



THE CONTENTS OF THE ROCKS. 



The contents of the rocks receive the general 

 name of fossils, from the Latin fossus, dug, because 

 they require generally to be dug out of the earth. 



Fossils may be divided into two great classes 

 animals and plants. 



Fossil Animals. In the rocks we discover spe- 

 cimens of every class included in the animal king- 

 dom. We find corals of all kinds, and of the most 

 beautiful structure, some branched like some of 

 the corals of the present seas, others standing in 

 masses on the very spots where they lived and 

 died, their remains giving beauty to our finest 

 marbles. We see star-like creatures of all kinds, 

 either spreading abroad their arms or curled up 

 at rest, as they may be seen any day during the 

 ebb of tide. Shells of every form, size, and colour 

 meet us at every step, as distinct as we now find 

 them on the shore ; and some formations, of vast 

 thickness and extent, are formed entirely of the 

 habitations of these little creatures. We may also 

 gather crustaceans, such as the crab and the lob- 

 ster, the minutest parts of their structure being 

 perfectly preserved. We discover fishes of every 

 kind and size, sometimes entire, as they fell to the 

 bottom at death, or crushed and broken in the 

 convulsions to which the rocks have been sub- 

 jected. We can gather the hard scales, that 

 defended them like armour ; can form collections 

 of their teeth, their fins, their jaws, and their eggs ; 

 and can construct them again as they swam about 

 in the ancient seas. Insects, too, we can gather 

 of every kind, and can see them as they flew about 

 in the old forests, and got entangled in the resin of 

 the great old trees. Birds, too, are found, though 

 not so plentifully as other creatures, as, from their 

 manner of life, they were not so easily carried 

 down by rivers, and deposited in the mud at their 

 mouths. We find reptiles of immense size, croco- 

 diles, and lizards, and flying dragons, with their 

 terrible teeth, sweeping tails, and adamantine 

 hides. We come upon beasts of every size, from 

 little creatures that burrow in the ground, to 

 gigantic deer, elephants, rhinoceroses, and mam- 

 moths; and may enter the very dens in which 

 lived beasts of prey, and to which they bore their 

 captured victims. 



These creatures differ more or less from those 

 that now inhabit the globe, but they are members 

 of the same classes ; and catalogues of them have 

 been formed as of those of the present day. A 

 visit to a museum in which fossils are exhibited 

 astonishes every one with the multitude, variety, 

 and beauty of those fossil creatures, and especially 

 with the wonderful preservation of organisms the 

 most delicate and frail. 



Fossil Plants. But the vegetable kingdom is 

 as fully represented in the rocks as the animal. 

 We find trees of the most varied kinds, with their 

 roots, stems, branches, leaves, flowers, and fruit. 

 We can look with wonder on the exquisite carving 

 on the stems of mighty trunks, hundreds of feet in 

 height, that once formed forests as dense and im- 

 penetrable as those of the Amazon. But more, 

 we can behold the trees standing on the very 

 places in which they grew and waved their great 

 branches, and can trace their roots as they pene- 

 trate the soil beneath. We can also gather plants 

 of all kinds reeds, mosses, rushes, sea- weeds, and 

 beautiful ferns preserved entire, and spread out 

 on the rock as delicate and perfect as in the finest 

 herbarium. These fossil plants have, like the 

 fossil animals, been examined and classified by 

 botanists, and we possess elaborate volumes on 

 the botany of the remote ages when these plants 



