210 EDWARD CHARLESWORTH, ESQ., F.G.S., ETC., ON THE 



Earth composed? This evening I propose to invite the 

 Members of the Victoria Institute to the consideration 

 of some of the phenomena presented by one of those 

 materials, and that one is the substance known to mineralo- . 

 gists by the name " Silex." This substance under a 

 great variety of forms has a large share in the constitution 

 of that small portion of the Earth beneath the surface 

 accessible to human observation, and which, for the sake of 

 convenience rather than correctness, is called its " crust?' 

 In this crust then we find as forms of Silex, the beautiful 

 substance known as Rock-crystal, also Jasper, Carnelian, 

 Chalcedony, Agate, and many others ; but the form of Silex 

 with which everyone is familiar, and which in its mass 

 exceeds by millions of times all other varieties of Silex put 

 together, is flint, a material which in many parts of England 

 is found so valuable in road-making and in building ; many 

 of the churches in East Anglia owing their high preservation 

 and beauty to the flint stones so largely used in their con- 

 struction. A geological student going into one of the 

 numerous chalk quarries which are to be seen on both sides 

 of the Thames between Gravesend and London, has his 

 attention at once arrested by horizontal strata of flint stones 

 imbedded in the chalk ; these flint strata being separated by 

 three or four feet of chalk. Attached to these flints and some- 

 times enclosed in them are various fossils of the same species 

 as are found in the chalk, consequently the chalk and the 

 flint, though so entirely distinct mineralogically, must be 

 regarded as one geological formation. But flint does not 

 characterise the entire thickness of the chalk, being fouud 

 only throughout its upper portion. There its presence 

 furnishes the geologist with both mineral and zoological 

 evidence for the identification of the upper portion of the 

 great chalk formation ; and while on the one hand, mineralo- 

 gists and chemists have occupied themselves in attemptmg 

 to explain the solution of flint in an ocean which must have 

 been so highly charged with lime, and its precipitation from 

 time to time in the condition we now find it, paleontologists, 

 attracted by the numerous organic bodies it preserves, have 

 naturally been led to speculate upon what may be termed 

 the cretaceous aspect of a mineral to which they owe the 

 possession of some of the most interesting objects of their 

 study. Now flint is by no means peculiar to the chalk 

 formation, but the conditions under which it comes under our 

 notice in chalk, constitute a phenomenon of the highest 

 possible scientific interest. 



