100 
GEOLOGY OF THE SECOND DISTRICT. 
the New-York Survey, are the lowest beds of the Transition System; they rest immediately 
upon the Primary, and though among themselves there is no unconformability, yet in many 
minor districts they are quite disturbed and broken up, especially near the line of junction 
between the transition and primary rocks. As we recede from this line to the deeper parts 
of the transition, they become quite regular, being scarcely disturbed or moved from the 
original position in which they were deposited. 
As the rocks which constitute the lower part of the mass of the Transition system have 
hitherto received very little attention, it became necessary not only to investigate with great 
care their characters and relation, but also to provide them with suitable names. After having 
given them the attention and care they seemed to require, I have, with little hesitation, con¬ 
cluded that they belong to but one group. Although there is a great diversity in the litholo¬ 
gical characters, still the fossils appear to belong to but few' types, and to those which are 
strictly related to each other. In this single group, the fossils appear to be allied ; but when 
we leave the upper member, and pass to the Medina sandstone, we find a distinct change in 
the character of the fossils. It is here we first meet with the Fucoides harlani; but up to 
this rock, certain genera and species of shells run through the entire mass, as Leptsena, Or- 
this, Atrypa, Delthyris, &c. Although these genera are not confined to the lower rocks, yet 
certain species, with very few exceptions, are confined to this lowest group ; and it is not only 
so with the Testacea, but also with the Crustacea; thus, the species belonging to the genera 
Isotelus, Trinucleus, Calymene, Illenus, etc. are mostly confined to it. One remarkable 
Polyparia, known as the Fucoides demissus, appears to belong, so far as researches have yet 
extended, to these lower rocks. I do not, however, propose in this place to go into the cha¬ 
racters of this group : the individual members will be described in their proper places, when 
I shall give a full account of their fossils, and the characteristic features of the several rocks 
comj)osing them. 
The name which appeared the most appropriate to this group, is derived from the lake along 
wdiich they are so well developed, (I refer to Lake Champlain); hence it becomes the Cham¬ 
plain group. Although it would have been perhaps desirable to have selected one from a 
town or locality, still there appear to be no strong objections to its use and adoption. In the 
first place, all the rocks and masses, without exception, are found not far from its borders ; 
and besides this, the whole is so accessible, that it is no small recommendation to its adoption. 
The name, too, is one which may well be considered less local than any other which could be 
selected : it is, as it Avere, a national name. Surrounded as it is by allied rocks, and bordered 
by two States, and extending into one of the British Provinces, it appeared more likely to be 
sanctioned than one derived from any locality within the limits of the Second District. 
Following out the plan of the nomenclature for the rocks of New-York, I have considered 
that, for purposes of study, they might be arranged in four groups, as follows : Champlain 
group, at the base of the Transition system ; Ontario group, comprehending the rocks which 
lie upon its southern border for about fifteen or twenty miles ; the Helderbergh series ; and 
lastly, the Erie group, which completes the whole series of the system, extending up to the 
old red sandstone. These four groups are tolerably well defined : they are, at least, so loca- 
