62 Correspondence. 
ever studied what we know as Huronian rocks in Canada, and which 
owing to the often impossibility of separating them from the Laurentian, 
we have latterly included under the name pre-Cambrian. 
The Huronian of Canada is, so far as we know, wholly unfossiliferous, 
and largely metamorphic, and is unconformably overlain by rocks of 
lower Cambrian age. 
Now I have heard a great deal about the Taconic system but have 
never used the name, being unable to make out precisely what it was» 
Recently, however, Mr. Marcou has defined his view of the Taconic,^ 
which appears to be very different from that of Mr. Miller, while Pro- 
fessor Walcott seems to regard it in very much the same light as I have 
been obliged to regard the " Quebec group," and I may say that I fully 
concur in Mr. Walcott's views. Some of Mr. Marcou's Taconic near 
Quebec is certainly newer than Trenton limestone while Mr. Miller's 
Taconic commences below the Potsdam. These wide differences of 
opinion as to what Taconic really is are, I think, a strong argument in 
favor of adopting Professor Walcott's views on the " Use of the name 
Taconic," as expressed in the American Journal of Science, May, 1888. 
Alfred R. C. Selwyn. 
Otta-va, June i, iSSS. 
Lake beaches at Ann Arbor. Dr. Wooldridge and I have gone over 
the beaches in the region of Ann Arbor. I fully concur with him that 
the Ann Arbor terrace is one of construction at the mouth of the Huron 
River (of that time) which now bends abruptly there. In short it is rather 
a terrace delta deposit between clay islands; and the cut terrace plain 
below, or the old lake bottom extends for some miles. Yours, etc., 
J. W. Spencer. 
Dr. Wm. Clark of Berea, (9., lias been continuing his enthusiastic and 
successful researches in the Ohio shale and has now the most remarka- 
ble collection of fossil fish (.') that has perhaps ever been brought together 
in America. He is already known to palaeontologists as the discoverer 
of the huge fossil described by Dr. J. S. Newberry at the meeting of the 
B. A. A. S. at Montreal, in 1884, and on which in honor of the finder was 
placed the name Titanichthys clarki. This measures about fifty-six inches 
across the head-shield and was the largest relic of a so-called fish that 
had, up to that date, been obtained from any part of the world. But the 
labors of 1886 and 1887 have been rewarded by other specimens of parts 
of this monster — a second head-shield surpassing the first and measur- 
ing seventy-one inches in breadth by 69 inches in length — a mandible 
thirty-five inches long with perfect alviolar process and groove — a pair 
of mandibles, right and left, thirty -four inches long by five inches deep 
— a fourth nearly perfect and thirty-one inches in length — and the an- 
terior portion of a fifth, twenty inches long carrying a perfect tooth, and 
the base of a second in the socket. To these we must add a large median 
1 Memo, of the Boston Soc. of Nat. Hist., vol. iv, March, 1888. 
