i^(JlLDER CLAY; NEAR WATFORD. 



241 



too generally, as the effect of cataclysms and catastrophes only. Some 

 of the most important of these breaks have been taken, and properly 

 so, as the divisional marks of the rock-masses in the precise, but 

 arbitrary an-angement and classification into which it is always necessary 

 to bring the objects of every science. 



It was amongst these so-called Azoic, or Hypozoic rocks, that clay- 

 slate, mica-schist, hornblende-schist, gneiss, primary limestone, various 

 rocks included in the unmeaning term Grauwacke, and numerous meta- 

 morphosed rocks were, by early geologists, and indeed only a few years 

 since, jumbled confusedly together. Many of them have since been 

 proved to be merely altered deposits of Silurian, or even much more 

 recent age. 



ys^c have now, however, already began to sort and to arrange, to 

 study and to teach that which when complete, will be the grandest and 

 most interesting of all the lessons of Geology. 



This great accumulation of rocks, then, with which we have to deal 

 in this chapter, those between the Silurian formation and the crystalline 

 and unstratified fundamental granites and gneiss, has already been 

 divided by the American geologists, as by our own, into two groups; 

 the one containing no organic remains, as far as our present researches 

 show, the other containing traces of primitive forms of organized 

 beings. 



(To be coittinucd.) 



ON THE OCCUEEEjS'CE OE THE BOCLDER CLAY, OR 

 NORTHER^^ CLAY DRIFT, AT BRICKET ^VOOD, KEAR 

 WATEORD. 



Ry Joseph Pkestwich, Esq., E.R.S. 



The Boulder Clay is so seldom exposed in the neighbourhood of London, 

 that I think it may be desirable to point out a new locality where I 

 have met with it and where it may yet be seen, especially as I have 

 just found some points, connected with its position at this place, which 

 are of rare occurrence. The new line of railway from Watford to St. 

 Albans passes chiefly through gravel and chalk. At one place, however, 

 called Bricket Wood, about midway between those towns, there is a cut- 

 ting of some length, and twenty to thirty feet deep, entirely through 

 the Boulder Clay. The superposition of this clay, with regard to the 



