396 



GEOLOGY OF THE SOUTH EAST OF DORSETSHIRE. 



The conglomerate is composed of clay, fractured flints, 

 green plastic clay, pebbles, and iron stone, the curvilinear di- 

 rection of which is deserving of notice. It is seen in fig. 47 

 that the chalk, at its extremity, is worn into cavities, which 

 are filled with conglomerate. The portions of chalk are yel- 

 low, curved, and fractured, and, corresponding to them, the 

 lowest beds of plastic clay, which consists, in its upper mem- 

 ber, of a black sand, and in its lower, of a hard iron stone con- 

 taining hollows filled with crystals of iron, — is arched over the 

 chalk and broken, evidently proving that the chalk has been 

 pushed up so as to protrude through the super-incumbent de- 

 posits, which fill up the intervals between the domes of chalk, 

 and dip vertically between them, as they ought to do in the 

 supposition of a regular arch thus formed. The iron stone 

 being the hardest, and the chalk being acted upon by destruc- 

 tive agents, in one instance the former remains a perfect arch, 

 the chalk being removed. Now in these domes of chalk, that 

 rock is fractured and split, together with its imbedded flints, 

 as it is a little to the westward. In all these cases of derange- 

 ment, it is remarkable that the chalk is of a yellowish hue, 

 which Mr. Lyell conceives to be the result of the iron in the 

 super-incumbent beds ; but such can hardly be £he case, when 

 it is observed that these yellow lines are not external mark- 

 ings, but a portion of the solid matter itself. The chalk here 

 is evidently composed of alternations of yellow and white lay- 

 ers, and in many cases most beautiful fragments may be found, 

 in which the layers are concentric, the nucleus being a white 

 nodule, and the yellow lines curving round, like the simi- 

 lar wood-like markings in the Red Rock of the plastic clay, 

 (fig. 49). The strata are also distinguished by yellow part- 

 ings, and often on the surface there 

 are innumerable minute black spots, 

 together with elegantly branching den- 

 drites, the latter seeming to result from 

 the pressure of the colouring liquid in 

 the squeezing of the beds. This li- 

 quid seems to have been manganese in 

 solution. What connection there may 

 actually have been between the de- 

 rangements in the beds and these me- 

 tallic markings, is foreign to our sub- 

 ject ; but the white beds of chalk are 

 undisturbed, and the yellow fractured 

 concentric curves of yellow chalk and curved : and the change of colour 



round a nucleus of white. Natu-^ ft sufficient indication of the locali- 



ral size. Studland Bay. 



ties of disturbance. 



Another point to be remarked is, that 



