Before taking our leave of Mr Greenough, we feel disposed to state candidly, that his performance is one by no means calculated to advance his own reputation, or promote the interests of geology.... He appears to be totally unacquainted with the laws of evidence. With him the testimony of every mineralogist is of equal value; all are supposed to have been equally well informed, and to have studied the subject with equal care....
There has resulted from all this a kind of geological scepticism, which we regard in this instance as the index of a mind unaccustomed to philosophical induction, but which others may consider as the mark of free and independent thinking. It is calculated to disgust the adept, and to perplex the tyro. It has been publicly intimated, that the author is a gentleman of independent fortune, and that he has expended large sums in furnishing an extensive collection of minerals. These circumstances, while they aggravate his errors, and render him more dangerous as an authority, recall an expression of the late illustrious Playfair in reference to De Luc, 'to reason and to arrange, are very different occupations of the mind; and a man may deserve praise as a mineralogist, who is but ill qualified for the researches of geology'.
John Fleming, Review of Greenough's Critical Examination, Edinburgh Monthly Review, IV (1820), 571. Quoted in Leroy E Page, Diluvialism and Its Critics in Science and Religious Belief: A Selection of Recent Historical Studies, CA Cassell (Ed), pp. 220-1
It's as nice a summary of the characteristics of junk science and the dangers of speaking out of your area of expertise as you're likely to find. As a bit of background, Fleming was writing during the period when geology was going through some of its formative debates. One of the issues at stake was diluvialism: whether the principal cause of the formations of the face of the earth that we see today were caused by a giant, world-encompassing flood.*
*Guess which one? Hint: the source material for the claim was not noticeably peer-reviewed.**
**Although it's unfair to suggest that it's that straightforward. The actual debate was more complicated than that - see the wiki entry I've linked to above. It's just not as funny if I go into the whole messy reality now.