The revival of interest in nineteenth-century American art, pioneered by Barbara Novak and more recently expanded by scholars such as Angela Miller, Allan Wallach and now Wilton and Barringer, raises insistent questions about the ideological parameters of landscape painting that are particularly fraught when it comes to frontier imagery. Defining the land - its vastness, its inhospitality, its savagery - was the first step towards legitimating its appropriation. Manifest Destiny determined that the territorial expansion of the US (which caused the displacement of Native Americans) was not only justifiable, but also divinely ordained. This exhibition is strong on early nationalist imagery, but disappointingly unrepresentative when it comes to frontier aesthetics

Not entirely coincidentally, the Transcendental poet, William Cullen Bryant, described Thomas Cole's landscapes as "acts of religion." And indeed, the Hudson River School not only raises cultural issues of an ideological, moral, philosophical, literary, scientific and political nature but also, and especially, issues of theological purpose, all of which presuppose an umbilical connection between the wilderness and God. Perceiving the 'Oversoul' everywhere, Cole, widely accepted as the father of American landscape painting, understood the wilderness as the 'undefined works' of the Creator. Even the geologist, John Wesley Powell, who led the first expedition through the Grand Canyon in1873, accompanied by the painter Thomas Moran, conceived the "canons of this region as a Book of Revelations in the rock-leaved Bible of geology." But if the divine order of the universe was particularly apposite to the landscape painters of the1840s and 1850s, ultimately it was replaced by Charles Darwin's theories of evolution. In this vein, Thomas Moran, travelled to Wyoming and Montana with the US Geological and Geographical Survey in 1871 where he produced a number of remarkable paintings of the Yellowstone and Colorado canyons - huge canvases exhibiting virtuoso powers of conception and skill. Moran's work is matched by that of Albert Bierstadt who had joined Frederick W. Lander's expedition in 1859, travelling through Kansas and Nebraska, to the Rocky Mountains. In these paintings, dramatic chiaroscuro alternately obscures and reveals towering rocks, deep chasms, splintered trees, thundering waterfalls, the visual effects of which are heightened by giddyingly low or high vantage points, saturated with glaring bursts of sunshine, sprayed with cascading water or illuminated with apocalyptic flashes of lightening.

William Clark and Captain Meriwether Lewis were appointed by Thomas Jefferson to conduct a transcontinental overland expedition to trace the course of the Missouri, from Saint Louis to the Rocky Mountains, and from the Continental Divide to the Pacific Coast, from 1804-1896. They documented the area - the flora and fauna, the geology and anthropology of the New World - causing them to invoke the concept of the Sublime. But nature, as William Cronon once observed, is not "nearly so natural as it seems...it is a profoundly human construction." Essentially, from the early Hudson River artists (such as Cole,) through the Luminists (as exemplified by Frederick Church), and the Transcendentalists (such as Fitz Hugh Lane), American landscape painting in the middle decades of the nineteenth-century must be seen in the context of Edmund Burke's concept of the Sublime.

In 1757, Edmund Burke maintained that "the passion caused by the great and sublime in nature... is astonishment; and astonishment is that state of the soul, in which all its motions are suspended, with some degree of horror." He went on to declare that terror is "the ruling principle of the sublime." According to Burke, "Whatever is fitted in any sort to excite the ideas of pain or danger, that is to say, whatever is in any sort terrible, or is conversant with terrible objects, or operates in a manner analogous to terror, is a source of the sublime that is it is productive of the strongest emotion which the mind is capable of feeling."

The Hudson River artists tended to concentrate on the Hudson River, west to the Catskills, and further on to the Niagara Falls; as well as the White Mountains of New Hampshire and Massachusetts. Mountains, cliffs, forests, cascading waterfalls, sheer rock, plunging vistas - paradoxically, their parochialism was national in scale. Cole's work, in particular, was considered definitively national. And yet, they are of the European tradition of Claude Lorrain and Salvator Rosa. Their problem was a style rooted in Rosa and Claude, or even Turner and Constable, but situated in new territory, with a different history. And while the terrain was novel, by and large, the artists (with the exception of Moran) were not compositionally innovative.

Integrated into the Sublime was the significance of historical and literary ideas, known as 'associationism'. Initially, the American landscape did not appear to lend itself to association, being considered devoid of meaning and history. Notwithstanding the real evidence countering this deficiency, explorers, writers and artists attempted to describe a constructed American landscape in European terms, thereby appropriating qualities associated with civilisation and ascribing them to the New World. The allegorical significance of Cole's Course of Empire is one remarkable, but far from subtle, result.

Niamh O'Sullivan is a lecturer in art history at NCAD, cuurently working on late nineteenth century Irish-American art.

American Sublime: Landscape Painting in the United States 1820-1880, Tate Britain, February-May 2002