124 DESCRIPTION OF THE STRATA. 



The imbedded fragments are still more diversified than the base 

 that includes them. Some are calcareous, others siliceous, others 

 argillaceous ; some are hard, others soft ; some are crystalline and 

 transparent or translucent, but the greater part are earthy and opaque \ 

 some are flat, but more are roundish ; some have sharp angles, but a 

 greater number are smooth or blunted; some have the appearance of 

 concretions, like the ova of the oolite, but most of them seem to 

 have once belonged to other rocks. They are of all sizes, from the 

 most minute grain, to the size of a pigeon's egg, which they rarely 

 exceed. They also exhibit a great variety of colour, most of them 

 being whitish, giving the stone a speckled appearance ; whilst many 

 of them, especially the larger pebbles or fragments, are of a dusky 

 colour, and others black, blue, green, &c. Of the crystalline frag- 

 ments, some consist of siliceous crystals, others of calc spar. Many 

 of the white specks in this stone appear to have resulted from the 

 decomposition of such crystalline fi-agments. 



Besides the crystalline substances derived from pre-existing 

 rocks, there are other crystals in many specimens of the dogger that 

 seem to belong to the stone itself, or that have been formed in it. 

 Some of these crystals are diffused through the stone, others are 

 collected in thin masses. The most singular mineral found in the 

 latter state is galena or lead-glance, which exists in slender veins, or in 

 crevices, accompanied with a sparry substance. It has its usual 

 metallic lustre, and lamellar structvire; but is found in very small 

 quantity. The authors have observed it only between Whitby and 

 Saltwick, and above the alum works at Sandsend. 



In many places the dogger consists of but one bed, which 

 is thick and hard; but very often it is divided into several hedc. 

 The stone, whether consisting of one bed or more, is very frequently 

 split into numerous blocks, by vertical partings or cross fissures. 

 These fissures or cracks, however, are not open, but filled with thin 



