BOULDER CLAY, iNEAK ^VAT1•0KD. 
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 arrangement 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 Grauwackc, and numerous meta- 
morphosed rocks were, bj^ 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 Kiluriun, or even much more 
recent age. 
We 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 unstratilied 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 tracts of primitive forms of organized 
beings. 
( To be vonlinued.) 
ON THE OCCURRENCE OF THE BOULDER, CLAY, OR 
NORTHERN CLAY DRIFT, AT BRICKET WOOD, NEAR 
WATFORD. 
By Joseph Pkestwicct, Es(][., F.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 
