194 



On Formations. 



[March^ 



iimcstonej which has a white colour^ is fine, earthy, and almost 

 friable. Tlirougliout its whole extent it is intermixed with small 

 river shells, which still retain their natural shell. Small reeds 

 also occur every where in this bed. It is the most characteristic 

 and extensive rock of the whole formation. In the middle of it 

 we meet with beds of smoke-grey hornstone, which has a fine 

 splintery, or imperfect conchoidal fracture. These beds are the 

 more remarkable, from the circumstance of siliceous beds oc- 

 curring very rarely in the limestone of Jura ; and when they do 

 appear, are never so pure and distinct as in the partial formation 

 of Locle. Tlie same species of fresh water shells as occur in the 

 marly limestone, also appear in tlie hornstone : amongst these 

 can be distinguished the Helix cornua, a species frequent in the 

 Lower Slhioe, but which has not lutherto been found in Switser- 

 land. Below the iiornstone lies a bed of opal, which is of a 

 brovvnisii bkick colour, glisterang lustre, and perfect conchoidal 

 fracture. This, Yon Buch observes, is a remarkable production 

 to be formed in the water of a lake; and is, in his opinion, a 

 Iiornstone coloured witli the coaliy matter of decayed vegetables. 

 To this opal succeeds a bed of bituminous shale, which contains 

 many impressions of reeds ; and next, a bed of coal, including 

 numen^us bivalve sliells. This coal burns badly; yet it is used 

 by blacksmiths, when a strong fire is required. These beds are 

 in general but a few inches thick, but alternate two or three 

 times as we descend ; and it is said they sometimes attain the 

 thickness of two feet. Tfie whole of these minerals are the 

 produce of a small inclosed lake ; for not a trace of these rocks 

 is to be seen beyond the mountains that surround Locle. We 

 thus see what lakes have produced : hills of 300 feet in height, 

 and compact siliceous beds which are almost crystalized. , Indeed, 

 crystals of quartz sometimes occur in the fissure of the hornstone. 



Another very curious local formation occurs at iEningen, on 

 the Rhine. The remarkable limestone rocks of that spot have 

 long engaged the particular attention* of mineralogists. The 

 celebrated quarries of /Eningen were said to contain organic 

 remains from every quarter of the globe, and in them it was 

 supposed we could read the whole history of the earth. The 

 acute and learned Bhimenbach, however, after examining this 

 formation, conjectured that it v^'as of very new date ; that it 

 was formed by one of those partial local revolutions which^ 

 according to him, have taken place since what he calls the last 

 general catastrophe which, our earth has experienced. Von Buch 

 is of opinion that it is a local formation, a deposition which had 

 taken place in a ])reviously existing lake from the rivers and 

 rivulets having deposited slime from the adjacent country over 

 fishes, insects, leaves, and other organic bodies, and gradually 

 enveloped tliem ia thin beds of mud : probably long after these 



