LESSONS IN GEOL< 



158 





*~ ' ;: 



LESSONS IN <M Y. -.\.\VI. 



i-i.i... ri.uiODS. 



IN the foHHJln yiolilod by tho deposits of thin period, more than 



on.'-hjilf urc found t" !" ivr.-nt or r\i-ting species. The 



:ueagroly represented in England. In tho 



Suffolk and Essex are found beds of soft marly 



> .in. Is l>.-li.ii:.:ini: t<> tliis age, containing large numbers of sheila, 



<_ i In- thickness of some fifty or sixty feet. They have 



. |i;--r,| tint ].roviin-i:il name of "crag," and are used by the 



to fertilise those heavy soils which are deficient in cal- 



. > matter. On the Continent tho Pliocene deposits attain 



magnitude. The Subapennino hills of Italy are accumu- 



of these beds, reaching a thickness of 2,000 feet ; and in 



t of Europe, to tho north of the Black Sea, and stretching 



1 tho Caspian and Sea of 



Aral, i< a widely-extended Plio- 



:irea. 



In Knijlaml the Pliocene beds 

 are divided into two 



1. The White or Coralline Crag. 

 H. The Bed Crag. 



The Coralline crag was tho 

 first formed. It only extends 

 in a narrow belt for about 

 twenty miles between the rivers 

 Aide and Stonr. It consists of 

 a mass of broken shells and 

 corals, which occasionally agglo- 

 merates into a soft building 

 stone. Although called coral- 

 lino crag, corals (as they are 

 now defined) are not frequently 

 found in it. Tho great mass of 

 the fossils are bryozoa, or rather 

 bryozoaria that is, structures 

 built up by colonies ot bryozoa. 



The term bryozoa (animal 

 moss) was first used by Ehren- 

 berg to denote those zoophytes 

 of which the Flustra and 

 Eschara are examples. These 

 differ from the coral zoophytes 

 in having two openings to the 

 digestive sac instead of one. 



In Fig. 154 wo give a speci- 

 men of a bryozoaria, the Fasci~ 

 cularia aurantium. Each of 

 the little punctures over the 

 surface was the home or cell of 

 a bryozoum. Probably by means 

 of tentacles tho animal caused 

 a current of water to pass into 

 its sac, and here not only was 

 all tho organic matter upon 

 which it existed abstracted 

 from the water, but also tho lime 



which the water held in solution by virtue of the presence of car- 

 bonic acid gas, and with the lime the zoophyte added something 

 t^ the structure which was tho common work of the colony. 

 Tho section we give shows how the work increased from a point 

 one generation building upon the cells in which their fathers 

 lived and died. Tho same process is in operation to-day on tho 

 coral-reefs. The prolific growth of the echini, the presence of 

 bryozoa, and tho evidences we have of the existence of a multi- 

 tude of testacea, prove that the Coralline crag must have been 

 deposited in tho tranquil waters of a deep sea. The tempera- 

 ture did not reach extremes, and was not tropical, for we find 

 one of the most characteristic of the Coralline crag shells is the 

 Astarte Omalii, which is a Northern form (Fig. 155). 



The Red crag was probably formed when the sea was more 

 shallow, and when the climate began to change prior to tho 

 sotting in of tho Glacial period, when an Arctic cold extended 

 pver Europe. Remains of the mastodon have been yielded by 

 tho crag, and some of the more prominent of its fossils are 

 Temnechinus excavatus (Fig. 156), Terebratula grandis (Fig. 

 157), Cardita senilis (Fig. 158), Valuta Lamberti (Fig. 159). 



144 N.E. 



Tho Norwich crag, which u ometimM called the JfammoK. 

 ferotu crag, because of the number of m%mmfJ remain* which 

 it contain*, u found in the neighbourhood of Norwich. It* 

 hell* are much more recent than the Coralline crag*, and moro 

 northern than those of tho Hod crag. Near Bridlington, on the 

 coast of Yorkshire, u another deposit of a umilar age. Tbeee 

 and tho Forout-bod are sometime* ola*od under the Port- pliocene. 



The Parent bed occupies near Cromer the position of the 

 Norwich crag. It in an ancient forest which wa labmerged 

 beneath the sea-level, and then Hands and clay* were deposited 

 upon it. The forest ha* been traced forty mile*. The *tnmp* 

 of the trees are still in their upright position* : they are Scotch 

 firs, yew, sloe, alder, and oak. These bed* contain the remain* 

 of the elephant, mammoth, rhinoceros, hippopotamus, bearer, 

 bear, deer, and other mammals. 



THE PLEISTOCENE PEBIOD, 



or, as it in now generally called, 

 tho Pott-pliocene, i* the upper- 

 most, and one of the most inter- 

 esting of the stratified deposit* 

 The Northern Drift. In 

 those countries which lie north 

 of latitude 50 i* found a most 

 peculiar deposit. It ha* re- 

 ceived various names Northern 

 drift, Diluvium, Boulder day, 

 Glacial deposits and it is 

 known in Scotland as Till. It 

 is a heap of debris of sand 

 and clay, sometimes stratified 

 more often not mixed with an- 

 gular fragments of the rock of 

 the neighbourhood. Sometime* 

 these fragments are actually 

 polished on one side, and the 

 flat surface exhibits parallel 

 scratches. 



Whenever the drift rest* di- 

 rectly on hard rock, such aa 

 granite, the face of the rock is 

 found smoothed and striated 

 similarly to the fragments. 

 Moreover, in many parts of the 

 British Isles the rocks of a 

 valley are found smoothed and 

 scratched. Take for example 

 tho neighbourhood of Snowdon. 

 Six valleys radiate from the 

 apex of the mountain, and in 

 each of these valleys the rocks 

 are all smoothed, and those 

 which protrude above the sur- 

 face of the ground near the bot- 

 tom of the valleys are rounded. 

 The scratching^ are always 

 parallel to the direction of tho 

 valley, and have evidently been 

 made by some hard substance 

 which filled the valley being dragged forcibly through it, a 

 process which must have frequently been repeated, for one set 

 of scratches may often be seen covering another older set, which 

 have another inclination, or are not quite parallel to the new 

 ones. These appearances were attempted to be explained by 

 those who called the drift Diluvium, upon the supposition that 

 they were the effects of the Flood ; that when the " fountains 

 of the great deep were broken up," surges of water rushed 

 over the surface of the land, leaving heaps of gravel, and 

 hurrying masses of rock through the valleys, scratching their 

 sides. 



But this explanation is evidently unsatisfactory ; moreoyer, 

 it is quite incapable of accounting for erratic blocks. Scattered 

 over the country are blocks of rock they are of all sizes, all 

 shapes, and are found in all positions. They are generally not 

 of the same kind as tho rock of the country, but have, by some 

 means or other, been transported many miles. Blocks of granite 

 and gneiss from the Highlands are found fifty or sixty miles 

 south. The "boulders," as they are called, which strew 

 Lancashire, Cheshire, Shropshire, and Staffordshire, evidently 



