22 BULLETIN OF THE 



at least ninety-five per cent of the recognizable fossils are members of 

 this group. Some of the layers at that locality which have an aggre- 

 gate thickness of half a foot are in good part composed of these remains. 

 It is interesting to note the fact, that certain of these species appear to 

 have found lodgment in the empty shells of their predecessors. In no 

 other way can we so well explain the fact, that from one to four of the 

 cones are often found packed into the larger shells in the manner indi- 

 cated in the diagrams of the descriptions of fossils from this section. 

 If this view of the relations of these included cones be correct, we have 

 in this horizon perhaps the first evidence of a habit of a somewhat intel- 

 lectual nature which is known through the history of the rocks. 



It is perhaps worth while to note that one of the Ptychoparias found 

 in this section is clearly rolled, as is the fashion with many of the forms, 

 such as the Calymenes, in higher horizons. This peculiar habit has been 

 supposed to be of a protective nature, the trilobite thereby securing im- 

 munity from danger when assaulted by enemies. This indeed seems at 

 first sight a very probable interpretation of this habit, and of the peculi- 

 arities of form which make the means of rolling the body into a ball 

 possible. The difficulty, however, is to see what was the nature of the 

 enemies from which the creature had to defend itself. The rocks of this 

 horizon are not known to contain any creatures capable of threateniug 

 the safety of the trilobites. So far as our knowledge goes, they were 

 themselves the only highly organized forms in this horizon. The other 

 creatures appear to have been relatively weak ; none of them, so far as 

 we know, were able to menace the trilobites, nor does it seem likely that 

 the trilobites could have assailed each other in a serious manner. 



Relation of this Deposit to Cambrian Problem. 



The position of these Attleborough beds with reference to the fauna of 

 the Paradoxides section is one of extreme interest. As yet these two 

 horizons have never been found in definite relations with each other, so 

 that it may be affirmed which of the two is the earlier. The Scandi- 

 navian geologists claim that in their country the Paradoxides zone oc- 

 cupits a higher position than that of the Olenellus group. On this 

 account I have taken much pains in seeking for any indication of 

 beds which could be referred to the Paradoxides zone. So far, I have 

 not succeeded in finding any trace of rocks whicn would serve to es- 

 tablish the relation between the two horizons. As is well known, a 

 considerable mass of strata, having an aggragate thickness of some 



