260 EAMBLES OF A GEOLOGIST. 



The Blackpots deposit is evidently a re-formation of a Liasic 

 patch, identical, both in mineralogical character and in its 

 organic remains, with the lower beds of the Eathie Lias ; 

 while the fragments of shale which it contains belong chiefly 



were struck, by the workman's shovel, we immediately commenced, and, 

 like an inquisitor of old, knocked our victims on the head, that they might 

 reveal their secrets ; or, like a Roman haruspex, examined their interior, 

 not, however, to obtain a knowledge of the future, but only to take a peep 

 into the past. 1. Here, then, we take up, not a regular Lias lime nodule, 

 but what appears to have formed part of one ; and the first blow has laid 

 open part of a whorl of an Ammonite, which, when complete, must have 

 measured three or four inches in diameter, and it is perfectly assimilated 

 to the calcareous matrix. 2. Here is a mass of indurated clay ; and a 

 gentle blow has exposed part of two Ammonites, smaller than the former, 

 but their shells are white and powdery like chalk. 3. Another fragment is 

 laid open ; and there, quite unmistakeably, lie the umbo and greater portion 

 ofihePlagiostomaconcentricum. 4. Another fragment of a granular gritty 

 structure presents a considerable portion of the interior of one of the shells 

 of a Pecten, but whether the attached fragment is part of one of its ears, 

 or of the other valve turned backward, is not so easily determined. 6. 

 Here is a piece of Belemnite in limestone, and the fracture in the fossil pre- 

 sents the usual glistening planes of cleavage. 6. Next we take up a piece 

 of distinctly laminated Lias, with Ammonites as thick as they can lie on 

 the pages of this black book of natural history. 7. Once more we strike, 

 and we have the cast and part of the shell of another bivalve ; but the valves 

 have been jerked off each other, and have suffered a severe compound frac- 

 ture ; nevertheless we can have little hesitation in pronouncing it a spe- 

 cies of unio. 8. Here is another piece of limestone, with its small frag- 

 ment of another shell, of very delicate texture, with finely marked traverse 

 striae. We are unwilling to decide on such slight evidence, but feel in- 

 clined to refer it to some species of Plagiostoma. 9. Here is a piece of 

 pyrites, not quite so large as the fist, and so vegetable-like in its markings, 

 that it might be mistaken for part of a branch of a tree. This is also cha- 

 racteristic of the Lias ; for when the shales are deeply impregnated with 

 bitumen and pyrites, they undergo a slow combustion when heaped up with 

 faggots and set on fire ; and in the cliffs of the Yorkshire coast, after rainy 

 weather, they sometimes spontaneously ignite, and continue to burn for 

 several months. 10. As we passed through the works, on our way to the 

 clay, we observed a sort of reservoir, into which the clay, after being freed 

 from its impurities, had been run in a liquid state ; the water had evapo- 

 rated, and the drying clay had cracked in every direction. Here we find 

 its counterpart .in this large mass of stone ; only the clay here, mixed with 

 a portion of lime, is petrified, and the fissures filled up with carbonate of 

 lime ; thus forming the septaria, or cement-stone. We have dressed a spe- 

 cimeH of it for our guide, who has a friend that will pojish it, when the 



