44 



a dark grey or bluish tinge, generally free from any organic nucleus. The 

 fossils are contained either in those portions that are most argillaceous and 

 which have striation ; or else on the exterior of the concretions. Their 

 formation, like that of most nodules and concretions, is due to the 

 segregation of particles, the agency being Molecular attraction. It may 

 not be deemed inapposite to quote a valuable passage bearing on this point 

 from the work of a gentleman whose name we have the honour to inscribe 

 on the muster roll of our Cotteswold Society. 



Professor Daitbent, in his treatise on the Atomic Theory, Ed. 2, p. 314, 

 1850, speaking of cohesive attraction, says, " Such a force seems to be 

 evinced in several well-known phenomena. It is shewn, for instance, in 

 the tendency which camphor and other volatile substances have, when 

 they sublime to collect around certain nuclei, on the surface of the 

 containing vessel, instead of spreading themselves equally throughout. It 

 is evinced also, if it be true, that an intimate mixture of finely comminuted 

 clay and sand, such as is used in the common operations of pottery, 

 cannot be left together for any length of time, without having the silicious 

 particles collected in certain parts of the mass more than in others." It 

 seems to me a case in point; look at the finely comminuted particles of 

 the shales whence this attractive force has sucked out when of course in 

 solution, all the silica, to form these concretionary geodes. This will be 

 an answer to the question, " Which was the prior formation, the limestone 

 or the shales?" The chances are that the clay was first deposited from 

 a shallow or sluggish water of inconsiderable depth, and, when in a 

 semi-fluid or plastic state, the concretions were then elaborated under the 

 segregating agency of chemical affinity, and the lamination into shales 

 was finally superinduced by the gravity of the overlying mass. These 

 limestones are in the form of elongated geodes, and when calcined or 

 ground, are used for making Eoman cements, although those on Churchdown 

 Hill are not worked for the purpose, yet they contain silicate of alumina 

 in the proportion of from 30 to 50 per cent. 



Of three analyses of normal types of such argillaceous Limestones from 

 different localities in England, the mean per centage stands thus : 



(Carbonate of Lime, per cent . . 55* 

 Silicate of Alumina, „ . . 39'5 

 Oxide of Iron, &c. ,, . . 4'5 



NoETH QuAEET. The smaller, or North Quarry, is situated about 60 or 

 70 yards from the larger, and affords a better field of exploration : — the beds 

 are of slight altitude, and are, therefore, easily reached ; the shales also are 

 more perfectly laminated, splitting parallel to the plane of the beds, and 

 here the knife comes into requisition more than the hammer. Tou have 

 simply to detach leaf from leaf to disclose the ripple marks ; the Algoe spread 



